GHSA-mg3v-6m49-jhp3
MEDIUMWebOb's location header normalization during redirect leads to open redirect
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
webobReal-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
When WebOb normalizes the HTTP Location header to include the request hostname, it does so by parsing the URL that the user is to be redirected to with Python's urlparse, and joining it to the base URL. urlparse however treats a // at the start of a string as a URI without a scheme, and then treats the next part as the hostname. urljoin will then use that hostname from the second part as the hostname replacing the original one from the request.
>>> parse.urlparse("//example.com/test/path")
ParseResult(scheme='', netloc='example.com', path='/test/path', params='', query='', fragment='')
WebOb uses urljoin to take the request URI and joining the redirect location, so assuming the request URI is: https://example.org//example.com/some/path, and the URL to redirect to (for example by adding a slash automatically) is //example.com/some/path/ that gets turned by urljoin into:
>>> parse.urljoin("https://example.org//attacker.com/some/path", "//attacker.com/some/path/")
'https://attacker.com/some/path/'
Which redirects from example.org where we want the user to stay to attacker.com
Patches
This issue is patched in WebOb 1.8.8
Older versions of WebOb continue to be vulnerable to this issue, and should be avoided.
Workarounds
Any use of the Response class that includes a location can be rewritten to make sure to always pass a full URI that includes the hostname to redirect the user to.
Thanks
- Sara Gao
This issue was reported via the Pylons Project Security List
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | webob | all versions | 1.8.8 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for webob. 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 webob to 1.8.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mg3v-6m49-jhp3 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-mg3v-6m49-jhp3 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-mg3v-6m49-jhp3. 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-mg3v-6m49-jhp3 in your dependencies?
O3 detects GHSA-mg3v-6m49-jhp3 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.