GHSA-7r87-cj48-wj45
MEDIUMPotential Captcha Validate Bypass in flask-session-captcha
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.
Blast Radius
flask-session-captchaReal-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
Impact
flask-session-captcha is a package which allows users to extend Flask by adding an image based captcha stored in a server side session.
The captcha.validate() function would return None if passed no value (e.g. by submitting a request with an empty form).
If implementing users were checking the return value to be False, the captcha verification check could be bypassed.
Sample vulnerable code:
if captcha.validate() == False:
... # abort
else:
... # do stuff
Patches
A new version (1.2.1) is available that fixes the issue.
Workarounds
Users can workaround the issue by not explicitly checking that the value is False.
Checking the return value less explicitly should still work.
if not captcha.validate():
... # abort
else:
... # do stuff
if captcha.validate():
... # do stuff
else:
... # abort
References
https://github.com/Tethik/flask-session-captcha/pull/27
For more information
If you have any questions or comments about this advisory:
- Open an issue in the github repo
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | flask-session-captcha | all versions | 1.2.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for flask-session-captcha. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update flask-session-captcha to 1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-7r87-cj48-wj45 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 pinpoints whether GHSA-7r87-cj48-wj45 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-7r87-cj48-wj45. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-7r87-cj48-wj45 in your dependencies?
O3 detects GHSA-7r87-cj48-wj45 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.