CVE-2024-42353

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

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

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2024-42353 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.8.8); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-42353? CVE-2024-42353 is a medium-severity open redirect vulnerability in webob (pip), affecting versions <= 1.8.7. It is fixed in 1.8.8. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2024-42353? CVE-2024-42353 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of webob are affected by CVE-2024-42353? webob (pip) versions <= 1.8.7 is affected.
4. Is there a fix for CVE-2024-42353? Yes. CVE-2024-42353 is fixed in 1.8.8. Upgrade to this version or later.
5. Is CVE-2024-42353 exploitable, and should I be worried? Whether CVE-2024-42353 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-42353 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-42353? Upgrade webob to 1.8.8 or later.