fix: Various security fixes (#38103)

- Enforce org visibility on organization label read endpoints (private
org labels no longer leak to non-members).
- Block fork sync (`merge-upstream`) when the base repo is no longer
readable (stops pulling commits after a parent goes private).
- Remove `REVERSE_PROXY_LIMIT` / `REVERSE_PROXY_TRUSTED_PROXIES` from
the Docker `app.ini` templates (the `= *` default allowed
`X-WEBAUTH-USER` impersonation; reverse-proxy auth is now opt-in and
admin-configured).
- Enforce single-use TOTP passcodes across web login, password-reset,
and Basic-Auth `X-Gitea-OTP` (fixes a TOCTOU race and a stateless
replay).
- Re-check branch write permission for every ref in a push (the
pre-receive hook cached the first ref's result, letting a per-branch
maintainer-edit grant escalate to full repo write).

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

docker/root/etc/templates/app.ini

@@ -51,8 +51,6 @@ ROOT_PATH = /data/gitea/log
 [security]
 INSTALL_LOCK = $INSTALL_LOCK
 SECRET_KEY   = $SECRET_KEY
-REVERSE_PROXY_LIMIT = 1
-REVERSE_PROXY_TRUSTED_PROXIES = *
 
 [service]
 DISABLE_REGISTRATION = $DISABLE_REGISTRATION

docker/rootless/etc/templates/app.ini

@@ -48,8 +48,6 @@ ROOT_PATH = $GITEA_WORK_DIR/data/log
 [security]
 INSTALL_LOCK = $INSTALL_LOCK
 SECRET_KEY   = $SECRET_KEY
-REVERSE_PROXY_LIMIT = 1
-REVERSE_PROXY_TRUSTED_PROXIES = *
 
 [service]
 DISABLE_REGISTRATION = $DISABLE_REGISTRATION

models/auth/twofactor.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/pquerna/otp/totp"
 	"golang.org/x/crypto/pbkdf2"
+	"xorm.io/builder"
 )
 
 //
@@ -104,20 +105,43 @@ func (t *TwoFactor) SetSecret(secretString string) error {
 	return nil
 }
 
-// ValidateTOTP validates the provided passcode.
+// validateTOTP validates the provided passcode. It does not consume the passcode; all login
-func (t *TwoFactor) ValidateTOTP(passcode string) (bool, error) {
+// surfaces must go through ValidateAndConsumeTOTP so that a passcode cannot be redeemed twice.
+func (t *TwoFactor) validateTOTP(passcode string) (bool, error) {
 	decodedStoredSecret, err := base64.StdEncoding.DecodeString(t.Secret)
 	if err != nil {
-		return false, fmt.Errorf("ValidateTOTP invalid base64: %w", err)
+		return false, fmt.Errorf("validateTOTP invalid base64: %w", err)
 	}
 	secretBytes, err := secret.AesDecrypt(t.getEncryptionKey(), decodedStoredSecret)
 	if err != nil {
-		return false, fmt.Errorf("ValidateTOTP unable to decrypt (maybe SECRET_KEY is wrong): %w", err)
+		return false, fmt.Errorf("validateTOTP unable to decrypt (maybe SECRET_KEY is wrong): %w", err)
 	}
 	secretStr := string(secretBytes)
 	return totp.Validate(passcode, secretStr), nil
 }
 
+// ValidateAndConsumeTOTP validates the passcode and atomically records it as used so that the
+// same passcode cannot be redeemed more than once (RFC 6238 §5.2). It returns false for an
+// invalid passcode as well as for a replay, including the case where a concurrent request with
+// the same passcode won the race first. All TOTP login surfaces must go through this helper.
+func (t *TwoFactor) ValidateAndConsumeTOTP(ctx context.Context, passcode string) (bool, error) {
+	ok, err := t.validateTOTP(passcode)
+	if err != nil || !ok {
+		return false, err
+	}
+	// Conditional update: only a row whose stored passcode differs from this one is updated, so a
+	// replay (or a concurrent duplicate) matches zero rows and is rejected. The row lock taken by
+	// the UPDATE serializes racing requests, closing the read-validate-write TOCTOU window.
+	t.LastUsedPasscode = passcode
+	n, err := db.GetEngine(ctx).ID(t.ID).
+		Where(builder.Or(builder.IsNull{"last_used_passcode"}, builder.Neq{"last_used_passcode": passcode})).
+		Cols("last_used_passcode").Update(t)
+	if err != nil {
+		return false, err
+	}
+	return n == 1, nil
+}
+
 // NewTwoFactor creates a new two-factor authentication token.
 func NewTwoFactor(ctx context.Context, t *TwoFactor) error {
 	_, err := db.GetEngine(ctx).Insert(t)

models/auth/twofactor_test.go

@@ -0,0 +1,47 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package auth_test
+
+import (
+	"testing"
+	"time"
+
+	auth_model "gitea.dev/models/auth"
+	"gitea.dev/models/unittest"
+
+	"github.com/pquerna/otp/totp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTwoFactorValidateAndConsumeTOTP(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	key, err := totp.Generate(totp.GenerateOpts{SecretSize: 40, Issuer: "gitea-test", AccountName: "consume"})
+	require.NoError(t, err)
+
+	tfa := &auth_model.TwoFactor{UID: 1}
+	require.NoError(t, tfa.SetSecret(key.Secret()))
+	require.NoError(t, auth_model.NewTwoFactor(t.Context(), tfa))
+
+	passcode, err := totp.GenerateCode(key.Secret(), time.Now())
+	require.NoError(t, err)
+
+	// first use of a valid passcode succeeds
+	ok, err := tfa.ValidateAndConsumeTOTP(t.Context(), passcode)
+	require.NoError(t, err)
+	assert.True(t, ok)
+
+	// replaying the same passcode is refused, even when still inside the TOTP validity window
+	reloaded, err := auth_model.GetTwoFactorByUID(t.Context(), tfa.UID)
+	require.NoError(t, err)
+	ok, err = reloaded.ValidateAndConsumeTOTP(t.Context(), passcode)
+	require.NoError(t, err)
+	assert.False(t, ok)
+
+	// an invalid passcode is rejected without consuming anything
+	ok, err = reloaded.ValidateAndConsumeTOTP(t.Context(), "000000")
+	require.NoError(t, err)
+	assert.False(t, ok)
+}

routers/api/v1/api.go

@@ -505,6 +505,21 @@ func reqOrgOwnership() func(ctx *context.APIContext) {
 	}
 }
 
+// reqOrgVisible requires the organization to be visible to the doer, or a site admin
+func reqOrgVisible() func(ctx *context.APIContext) {
+	return func(ctx *context.APIContext) {
+		if ctx.Org.Organization == nil {
+			setting.PanicInDevOrTesting("reqOrgVisible: unprepared context")
+			ctx.APIErrorInternal(errors.New("reqOrgVisible: unprepared context"))
+			return
+		}
+		if !organization.HasOrgOrUserVisible(ctx, ctx.Org.Organization.AsUser(), ctx.Doer) {
+			ctx.APIErrorNotFound()
+			return
+		}
+	}
+}
+
 func teamAccessPrivileged(ctx *context.APIContext) (orgID int64, privileged, ok bool) {
 	if ctx.IsUserSiteAdmin() {
 		return 0, true, true
@@ -1728,7 +1743,7 @@ func Routes() *web.Router {
 				m.Combo("/{id}").Get(reqToken(), org.GetLabel).
 					Patch(reqToken(), reqOrgOwnership(), bind(api.EditLabelOption{}), org.EditLabel).
 					Delete(reqToken(), reqOrgOwnership(), org.DeleteLabel)
-			})
+			}, reqOrgVisible())
 			m.Group("/hooks", func() {
 				m.Combo("").Get(org.ListHooks).
 					Post(bind(api.CreateHookOption{}), org.CreateHook)

routers/api/v1/repo/branch.go

@@ -1336,6 +1336,9 @@ func MergeUpstream(ctx *context.APIContext) {
 		} else if errors.Is(err, util.ErrNotExist) {
 			ctx.APIError(http.StatusNotFound, err.Error())
 			return
+		} else if errors.Is(err, util.ErrPermissionDenied) {
+			ctx.APIError(http.StatusForbidden, err.Error())
+			return
 		}
 		ctx.APIErrorInternal(err)
 		return

routers/private/hook_pre_receive.go

@@ -40,9 +40,6 @@ type preReceiveContext struct {
 	canCreatePullRequest        bool
 	checkedCanCreatePullRequest bool
 
-	canWriteCode        bool
-	checkedCanWriteCode bool
-
 	protectedTags    []*git_model.ProtectedTag
 	gotProtectedTags bool
 
@@ -50,24 +47,36 @@ type preReceiveContext struct {
 
 	opts *private.HookOptions
 
-	branchName string
+	// this context should only contain shared variables, mutable variables like "current branch name" shouldn't be put here
+	canWriteCodeUnitCached *bool
 }
 
-// CanWriteCode returns true if pusher can write code
+func (ctx *preReceiveContext) canWriteCodeUnit() bool {
-func (ctx *preReceiveContext) CanWriteCode() bool {
+	if ctx.canWriteCodeUnitCached == nil {
-	if !ctx.checkedCanWriteCode {
+		var canWrite bool
-		if !ctx.loadPusherAndPermission() {
+		if ctx.loadPusherAndPermission() {
+			canWrite = ctx.userPerm.CanWrite(unit.TypeCode) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
+		}
+		ctx.canWriteCodeUnitCached = &canWrite
+	}
+	return *ctx.canWriteCodeUnitCached
+}
+
+// canWriteCodeRef returns true if pusher can write to the code ref (branch/tag/commit)
+func (ctx *preReceiveContext) canWriteCodeRef(refFullName git.RefName) bool {
+	if ctx.canWriteCodeUnit() {
+		return true
+	}
+	// then check whether if the pusher is a maintainer who can write the PR author's head repo branch
+	if !refFullName.IsBranch() {
 		return false
 	}
-		ctx.canWriteCode = issues_model.CanMaintainerWriteToBranch(ctx, ctx.userPerm, ctx.branchName, ctx.user) || ctx.deployKeyAccessMode >= perm_model.AccessModeWrite
+	return issues_model.CanMaintainerWriteToBranch(ctx, ctx.userPerm, refFullName.BranchName(), ctx.user)
-		ctx.checkedCanWriteCode = true
-	}
-	return ctx.canWriteCode
 }
 
-// AssertCanWriteCode returns true if pusher can write code
+// assertCanWriteRef returns true if pusher can write to the code ref, otherwise it responds with 403 Forbidden and returns false
-func (ctx *preReceiveContext) AssertCanWriteCode() bool {
+func (ctx *preReceiveContext) assertCanWriteRef(refFullName git.RefName) bool {
-	if !ctx.CanWriteCode() {
+	if !ctx.canWriteCodeRef(refFullName) {
 		if ctx.Written() {
 			return false
 		}
@@ -129,7 +138,7 @@ func HookPreReceive(ctx *gitea_context.PrivateContext) {
 		case git.DefaultFeatures().SupportProcReceive && refFullName.IsFor():
 			preReceiveFor(ourCtx, refFullName)
 		default:
-			ourCtx.AssertCanWriteCode()
+			ourCtx.assertCanWriteRef(refFullName)
 		}
 		if ctx.Written() {
 			return
@@ -141,9 +150,8 @@ func HookPreReceive(ctx *gitea_context.PrivateContext) {
 
 func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID string, refFullName git.RefName) {
 	branchName := refFullName.BranchName()
-	ctx.branchName = branchName
 
-	if !ctx.AssertCanWriteCode() {
+	if !ctx.assertCanWriteRef(refFullName) {
 		return
 	}
 
@@ -404,7 +412,7 @@ func preReceiveBranch(ctx *preReceiveContext, oldCommitID, newCommitID string, r
 }
 
 func preReceiveTag(ctx *preReceiveContext, refFullName git.RefName) {
-	if !ctx.AssertCanWriteCode() {
+	if !ctx.assertCanWriteRef(refFullName) {
 		return
 	}
 

routers/private/hook_pre_receive_test.go

@@ -0,0 +1,70 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package private
+
+import (
+	"testing"
+
+	issues_model "gitea.dev/models/issues"
+	"gitea.dev/models/perm/access"
+	repo_model "gitea.dev/models/repo"
+	"gitea.dev/models/unittest"
+	"gitea.dev/modules/git"
+	"gitea.dev/services/contexttest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestPreReceiveCanWriteCodePerBranch ensures the maintainer-edit write grant is evaluated against
+// the exact ref being pushed on every call, derived from that ref rather than shared mutable state.
+// Otherwise a per-branch grant (an open PR with "allow edits from maintainers") could be batched
+// together with a protected branch or a tag to escalate into full repository write.
+func TestPreReceiveCanWriteCodePerBranch(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	baseRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 10})
+	headRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 11})
+	require.NoError(t, baseRepo.LoadOwner(t.Context()))
+	require.NoError(t, headRepo.LoadOwner(t.Context()))
+
+	// An open PR from the head repo owner, with maintainer edits allowed: this grants the base
+	// repo owner write access to exactly this head branch and nothing else.
+	pr := &issues_model.PullRequest{
+		Issue: &issues_model.Issue{
+			RepoID:   baseRepo.ID,
+			PosterID: headRepo.OwnerID,
+		},
+		HeadRepoID:          headRepo.ID,
+		BaseRepoID:          baseRepo.ID,
+		HeadBranch:          "granted-branch",
+		BaseBranch:          "master",
+		AllowMaintainerEdit: true,
+	}
+	require.NoError(t, issues_model.NewPullRequest(t.Context(), baseRepo, pr.Issue, nil, nil, pr))
+
+	// The pusher is the base repo owner (the maintainer) with only read access on the head repo.
+	maintainer := baseRepo.Owner
+	headPerm, err := access.GetIndividualUserRepoPermission(t.Context(), headRepo, maintainer)
+	require.NoError(t, err)
+
+	mockCtx, _ := contexttest.MockPrivateContext(t, "/")
+	ctx := &preReceiveContext{
+		PrivateContext: mockCtx,
+		loadedPusher:   true,
+		user:           maintainer,
+		userPerm:       headPerm,
+	}
+
+	// The granted branch must be writable...
+	assert.True(t, ctx.canWriteCodeRef(git.RefNameFromBranch("granted-branch")))
+
+	// ...but another branch in the same push must NOT inherit that grant.
+	assert.False(t, ctx.canWriteCodeRef(git.RefNameFromBranch("master")))
+
+	// ...and a tag sharing the granted branch's name must NOT inherit it either: the grant is
+	// scoped to PR head branches, so a non-branch ref can never match it. (A tag ref already
+	// yields an empty branch name, so this guards the per-ref evaluation, not the IsBranch check.)
+	assert.False(t, ctx.canWriteCodeRef(git.RefNameFromTag("granted-branch")))
+}

routers/web/auth/2fa.go

@@ -58,14 +58,14 @@ func TwoFactorPost(ctx *context.Context) {
 		return
 	}
 
-	// Validate the passcode with the stored TOTP secret.
+	// Validate the passcode and atomically consume it to prevent reuse/replay.
-	ok, err := twofa.ValidateTOTP(form.Passcode)
+	ok, err := twofa.ValidateAndConsumeTOTP(ctx, form.Passcode)
 	if err != nil {
 		ctx.ServerError("UserSignIn", err)
 		return
 	}
 
-	if ok && twofa.LastUsedPasscode != form.Passcode {
+	if ok {
 		remember := ctx.Session.Get("twofaRemember").(bool)
 		u, err := user_model.GetUserByID(ctx, id)
 		if err != nil {
@@ -81,12 +81,6 @@ func TwoFactorPost(ctx *context.Context) {
 			}
 		}
 
-		twofa.LastUsedPasscode = form.Passcode
-		if err = auth.UpdateTwoFactor(ctx, twofa); err != nil {
-			ctx.ServerError("UserSignIn", err)
-			return
-		}
-
 		_ = ctx.Session.Set(session.KeyUserHasTwoFactorAuth, true)
 		handleSignIn(ctx, u, remember)
 		return

routers/web/auth/password.go

@@ -177,23 +177,17 @@ func ResetPasswdPost(ctx *context.Context) {
 			regenerateScratchToken = true
 		} else {
 			passcode := ctx.FormString("passcode")
-			ok, err := twofa.ValidateTOTP(passcode)
+			ok, err := twofa.ValidateAndConsumeTOTP(ctx, passcode)
 			if err != nil {
-				ctx.HTTPError(http.StatusInternalServerError, "ValidateTOTP", err.Error())
+				ctx.HTTPError(http.StatusInternalServerError, "ValidateAndConsumeTOTP", err.Error())
 				return
 			}
-			if !ok || twofa.LastUsedPasscode == passcode {
+			if !ok {
 				ctx.Data["IsResetForm"] = true
 				ctx.Data["Err_Passcode"] = true
 				ctx.RenderWithErrDeprecated(ctx.Tr("auth.twofa_passcode_incorrect"), tplResetPassword, nil)
 				return
 			}
-
-			twofa.LastUsedPasscode = passcode
-			if err = auth.UpdateTwoFactor(ctx, twofa); err != nil {
-				ctx.ServerError("ResetPasswdPost: UpdateTwoFactor", err)
-				return
-			}
 		}
 	}
 

routers/web/repo/branch.go

@@ -264,7 +264,7 @@ func MergeUpstream(ctx *context.Context) {
 	branchName := ctx.FormString("branch")
 	_, err := repo_service.MergeUpstream(ctx, ctx.Doer, ctx.Repo.Repository, branchName, false)
 	if err != nil {
-		if errors.Is(err, util.ErrNotExist) {
+		if errors.Is(err, util.ErrNotExist) || errors.Is(err, util.ErrPermissionDenied) {
 			ctx.JSONErrorNotFound()
 			return
 		} else if pull_service.IsErrMergeConflicts(err) {

services/auth/basic.go

@@ -177,7 +177,8 @@ func validateTOTP(req *http.Request, u *user_model.User) error {
 		}
 		return err
 	}
-	if ok, err := twofa.ValidateTOTP(req.Header.Get("X-Gitea-OTP")); err != nil {
+	// Consume the passcode atomically so a captured OTP cannot be replayed within its validity window.
+	if ok, err := twofa.ValidateAndConsumeTOTP(req.Context(), req.Header.Get("X-Gitea-OTP")); err != nil {
 		return err
 	} else if !ok {
 		return util.NewInvalidArgumentErrorf("invalid provided OTP")

services/repository/merge_upstream.go

@@ -8,7 +8,9 @@ import (
 	"fmt"
 
 	issue_model "gitea.dev/models/issues"
+	access_model "gitea.dev/models/perm/access"
 	repo_model "gitea.dev/models/repo"
+	"gitea.dev/models/unit"
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/git"
 	"gitea.dev/modules/gitrepo"
@@ -26,6 +28,17 @@ func MergeUpstream(ctx reqctx.RequestContext, doer *user_model.User, repo *repo_
 	if err = repo.GetBaseRepo(ctx); err != nil {
 		return "", err
 	}
+
+	// The doer must still be able to read the base repository's code. Otherwise a fork created
+	// while the base repo was public could keep pulling commits after it turned private.
+	basePerm, err := access_model.GetDoerRepoPermission(ctx, repo.BaseRepo, doer)
+	if err != nil {
+		return "", err
+	}
+	if !basePerm.CanRead(unit.TypeCode) {
+		return "", util.NewPermissionDeniedErrorf("permission denied to read base repo %d", repo.BaseRepo.ID)
+	}
+
 	divergingInfo, err := GetUpstreamDivergingInfo(ctx, repo, branch)
 	if err != nil {
 		return "", err

tests/integration/api_org_test.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	auth_model "gitea.dev/models/auth"
+	issues_model "gitea.dev/models/issues"
 	org_model "gitea.dev/models/organization"
 	"gitea.dev/models/perm"
 	repo_model "gitea.dev/models/repo"
@@ -292,3 +293,50 @@ func testAPIDeleteOrgRepos(t *testing.T) {
 		MakeRequest(t, req, http.StatusNoContent) // The org contains no repositories, so the API should return StatusNoContent
 	})
 }
+
+// TestAPIOrgLabelsVisibility ensures the organization label read endpoints honor
+// the organization visibility: labels of a private org must not be disclosed to
+// users who cannot see the org (GHSA: unauthorized access to private org labels).
+func TestAPIOrgLabelsVisibility(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	// privated_org (id 23) is a private organization; user5 is its only member.
+	privateOrg := unittest.AssertExistsAndLoadBean(t, &org_model.Organization{ID: 23})
+	label := &issues_model.Label{OrgID: privateOrg.ID, Name: "internal-label", Color: "#aabbcc", Description: "private organization label"}
+	require.NoError(t, issues_model.NewLabel(t.Context(), label))
+
+	listURL := fmt.Sprintf("/api/v1/orgs/%s/labels", privateOrg.Name)
+	getURL := fmt.Sprintf("/api/v1/orgs/%s/labels/%d", privateOrg.Name, label.ID)
+
+	t.Run("NonMemberDenied", func(t *testing.T) {
+		// user2 is not a member of the private org and must not see its labels.
+		token := getUserToken(t, "user2", auth_model.AccessTokenScopeReadOrganization)
+		MakeRequest(t, NewRequest(t, "GET", listURL).AddTokenAuth(token), http.StatusNotFound)
+		MakeRequest(t, NewRequest(t, "GET", getURL).AddTokenAuth(token), http.StatusNotFound)
+	})
+
+	t.Run("AnonymousDenied", func(t *testing.T) {
+		MakeRequest(t, NewRequest(t, "GET", listURL), http.StatusNotFound)
+		MakeRequest(t, NewRequest(t, "GET", getURL), http.StatusNotFound)
+	})
+
+	t.Run("MemberAllowed", func(t *testing.T) {
+		token := getUserToken(t, "user5", auth_model.AccessTokenScopeReadOrganization)
+		resp := MakeRequest(t, NewRequest(t, "GET", listURL).AddTokenAuth(token), http.StatusOK)
+		labels := DecodeJSON(t, resp, &[]*api.Label{})
+		assert.Len(t, *labels, 1)
+		MakeRequest(t, NewRequest(t, "GET", getURL).AddTokenAuth(token), http.StatusOK)
+	})
+
+	t.Run("SiteAdminAllowed", func(t *testing.T) {
+		token := getUserToken(t, "user1", auth_model.AccessTokenScopeReadOrganization)
+		MakeRequest(t, NewRequest(t, "GET", listURL).AddTokenAuth(token), http.StatusOK)
+		MakeRequest(t, NewRequest(t, "GET", getURL).AddTokenAuth(token), http.StatusOK)
+	})
+
+	t.Run("PublicOrgStillReadable", func(t *testing.T) {
+		// org3 (id 3) is a public org with labels; non-members may read them.
+		token := getUserToken(t, "user2", auth_model.AccessTokenScopeReadOrganization)
+		MakeRequest(t, NewRequest(t, "GET", "/api/v1/orgs/org3/labels").AddTokenAuth(token), http.StatusOK)
+	})
+}

tests/integration/api_twofa_test.go

@@ -51,6 +51,12 @@ func TestAPITwoFactor(t *testing.T) {
 		AddBasicAuth(user.Name)
 	req.Header.Set("X-Gitea-OTP", passcode)
 	MakeRequest(t, req, http.StatusOK)
+
+	// the same passcode must not be replayable on the basic-auth surface (RFC 6238 single-use)
+	req = NewRequest(t, "GET", "/api/v1/user").
+		AddBasicAuth(user.Name)
+	req.Header.Set("X-Gitea-OTP", passcode)
+	MakeRequest(t, req, http.StatusUnauthorized)
 }
 
 func TestBasicAuthWithWebAuthn(t *testing.T) {

tests/integration/repo_merge_upstream_test.go

@@ -171,5 +171,18 @@ func TestRepoMergeUpstream(t *testing.T) {
 			}).AddTokenAuth(token)
 			MakeRequest(t, req, http.StatusBadRequest)
 		})
+
+		t.Run("BasePrivateBlocksSync", func(t *testing.T) {
+			// add a new commit to the base repo, then make the base repo private
+			require.NoError(t, createOrReplaceFileInBranch(baseUser, baseRepo, "secret.txt", "master", "private-content"))
+			baseRepo.IsPrivate = true
+			_, err := db.GetEngine(t.Context()).ID(baseRepo.ID).Cols("is_private").Update(baseRepo)
+			require.NoError(t, err)
+			// the fork owner can no longer read the base repo, so syncing must be refused
+			req = NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/test-repo-fork/merge-upstream", forkUser.Name), &api.MergeUpstreamRequest{
+				Branch: "fork-branch",
+			}).AddTokenAuth(token)
+			MakeRequest(t, req, http.StatusForbidden)
+		})
 	})
 }