CVE-2026-39376 FastFeedParser has an infinite redirect loop DoS via meta-refresh chain
An attacker can cause a denial of service in FastFeedParser by triggering an infinite recursion loop via chained meta-refresh redirects.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39376?
CVE-2026-39376 is a high-severity denial of service vulnerability in kagisearch fastfeedparser, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
FastFeedParser is a high performance RSS, Atom and RDF parser. Prior to 0.5.10, when parse() fetches a URL that returns an HTML page containing a <meta http-equiv="refresh"> tag, it recursively calls itself with the redirect URL — with no depth limit, no visited-URL deduplication, and no redirect count cap. An attacker-controlled server that returns an infinite chain of HTML meta-refresh responses causes unbounded recursion, exhausting the Python call stack and crashing the process. This vulnerability can also be chained with the companion SSRF issue to reach internal network targets after bypassing the initial URL check. This vulnerability is fixed in 0.5.10.
Weakness: CWE-674
Which versions are affected by CVE-2026-39376?
3 open source packages ship an affected version, including fastfeedparser. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
fastfeedparser PyPI | All versions | 0.5.10 |
fastfeedparser PyPI | All versions | 0.5.10 |
fastfeedparser PyPI | All versions | 0.5.10 |
Products include Kagi Fastfeedparser.
How do I fix CVE-2026-39376?
Upgrade fastfeedparser to 0.5.10 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-39376 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39376 exists.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-4gx2-pc4f-wq37, PYSEC-2026-60.