CVE-2026-41425 — authlib
MEDIUMCVE-2026-41425 is a medium-severity (CVSS 5.4) Cross-Site Request Forgery (CSRF) vulnerability in authlib. A fix is available for authlib — see the affected versions and patch details below.
Authlib: Cross-site request forging when using cache
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-2026-41425.
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-2026-41425 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 378,567 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
authlibReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
There is no CSRF protection on the cache feature on most integrations clients.
Details
In authlib.integrations.starlette_client.OAuth, no CSRF protection is set up when using the cache parameter. When not using the cache parameter, the use of SessionMiddleware ties the client to the auth state, preventing CSRF attacks. With the cache, there is no such mechanism. Other integratons have the same issue, it's not just starlette.
The state parameter is taken from the callback URL and the state is fetched from the cache without checking that it is the same client calling the redirect endpoint as was the one that initiated the auth flow.
This issue is documented in RFC 6749 section 10.12: https://datatracker.ietf.org/doc/html/rfc6749#section-10.12
PoC
- Set up a Starlette integration with a cache
- The attacker starts the auth flow up until before the callback URL is followed.
- The attacked sends the redirect URL to the victim
- The victim now completes the authorisation
Impact
This impacts all users that use the cache to store auth state.
All users will be vulnerable to CSRF attacks and may have an attacker's account tied to their own.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | authlib | all versions | 1.6.11pip install --upgrade 'authlib==1.6.11' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for authlib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update authlib to 1.6.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41425 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-2026-41425 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-41425. 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-2026-41425 in your dependencies?
O3 Security finds CVE-2026-41425 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.