Tugtainer: Improper verification of OIDC ID token signatures
Summary
Tugtainer, a self-hosted app for automating Docker container updates, accepts OIDC ID tokens without verifying their signature, audience, issuer or expiry. The claims from the unverified token are used directly as the user identity for the Tugtainer session. An attacker in a position to supply or alter the token, such as a man-in-the-middle between the backend and the OIDC provider or a rogue provider, can log in as another identity and obtain a session with the privileges of that user. The vulnerability only applies when OIDC login is enabled.
Affected
- Tugtainer versions before 1.31.3 (vendor advisory lists <= 1.31.2)
- Only deployments with OIDC login enabled
Fixed in
- Tugtainer 1.31.3 (released 2026-08-06)
Workaround
- No vendor workaround. Patch to 1.31.3 or later.
- If patching is not possible immediately: disable OIDC login, and restrict access to the UI with a VPN, IP allowlist or authenticated reverse proxy.
Exploitation
- A public proof-of-concept repository is referenced for this advisory; its content was not reviewed.
- CISA SSVC: exploitation status poc, not automatable.
- No evidence of in-the-wild exploitation found; the CVE is not listed in the CISA KEV catalog.
Our recommendation
- Upgrade Tugtainer to version 1.31.3 or later.
- After upgrading, test OIDC login, because tokens with symmetric algorithms, mismatched issuer URLs or missing id_token may now be rejected.
- Check whether OIDC login is enabled and whether the UI is reachable beyond the LAN; prioritise instances that are exposed.
- Review the Docker socket mount, as a takeover may give control over the Docker host.
- Review access logs for unexpected OIDC logins.
Public exploits
Links to third-party sites, not checked by us – exploit code can contain malware. Only use it in isolated test environments.
- Proof of concept on GitHub (1 repositories)
squeeze440/tugtainer-PoC
Research sources
- Vendor advisory GHSA-crjc-6vc7-xrfh github.com
- Fix commit b55269b github.com
- Release v1.31.3 github.com
- OSV CVE-2026-87004 osv.dev
- CVE-2026-87004 on OpenCVE app.opencve.io
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 21:07.
Original description (NVD)
Tugtainer is a self-hosted app for automating updates of Docker containers. Prior to version 1.31.3, when the OIDC login flow completes, backend/modules/auth/providers/auth_oidc_provider.py decodes the id_token returned by the identity provider's token endpoint using jose.jwt.get_unverified_claims() instead of jwt.decode(). This skips signature verification, audience (aud) validation, issuer (iss) validation, and expiry (exp) checking entirely. The extracted claims (email/sub/preferred_username) are then used directly as the user_id for the resulting Tugtainer session. This issue has been patched in version 1.31.3.
NVD references (4)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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