CVE-2026-66853

Gitea's web attachment handler skips its cross-repository ownership check for attachments created before 16 January 2026 and checks permissions against the repository named in the request URL instead. An unauthenticated attacker who knows a private attachment's UUID can request it through a public repository's attachment path and retrieve its contents.

When OpenID sign-in is enabled, Gitea processes unauthenticated assertion parameters and sends an HTTP POST request to the caller-supplied OpenID provider endpoint during verification. An attacker controls the destination and much of the form body, allowing interaction with internal HTTP services reachable from the Gitea server.

Gitea's collaboration access-mode endpoint accepts the Owner access mode from an authenticated repository collaborator with Admin access. The collaborator can promote their effective permissions from Admin to Owner and then perform owner-only operations, including transferring the repository to their own account.

Gitea allows a token with write:user scope to register an attacker-controlled SSH public key on the token owner's account. API requests signed with the corresponding private key authenticate as that account through HTTP Signature without API token scope information, causing route-level token scope checks to be skipped.

Gitea resolves local reusable workflow files from a fork's head commit when a trusted base-branch workflow runs for a pull_request_target event. A fork author can modify a referenced reusable workflow so attacker-controlled code executes with the repository and organization secrets available to that event.

Gitea substitutes a URL derived from the markup Context field into external renderer command templates without escaping the reference path before shell-style argument splitting. A crafted Context can inject additional renderer arguments, including options that load executable filter files. On deployments using a susceptible external renderer such as pandoc, a user who can place a filter file at an accessible path can cause it to execute as the Gitea service account; the public repository markup endpoint itself can be reachable without authentication.

Gitea's OpenID connect handler accepts a user's password without enforcing enrolled TOTP or WebAuthn verification before completing sign-in and linking an OpenID identifier. When OpenID sign-in is enabled, an attacker who knows the victim's password can obtain a session and link an attacker-controlled identifier. The attacker can then sign in through that identifier without the victim's password or second factor, and a password change does not remove the link.

Gitea's Maven upload handler reads checksum uploads entirely into memory and returns before enforcing package-size quotas. An authenticated user with package-publish permission can submit an oversized body to a checksum endpoint, bypassing the upload quota and exhausting server memory.

Gitea uses inconsistent repository visibility predicates, and the condition used by some repository-listing endpoints admits repositories whose owners are hidden from the viewer. Those listings disclose repository metadata even though direct routes correctly deny access with a 404 response.

Gitea does not limit the length of the gitignores field accepted by repository-creation forms and the API. Repository initialization splits the field into template names, repeatedly reads the referenced templates, and buffers their contents in memory. An attacker who can create repositories can submit an oversized value to amplify template reads and memory use, impairing availability.