CVE-2026-39376: FastFeedParser has an infinite redirect loop DoS via meta-refresh chain

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-04-07 · updated 2026-07-24
Weakness: CWE-674

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.

Affected products

kagisearch fastfeedparser: before 0.5.10 — fixed in 0.5.10

How to fix

Upgrade to a fixed version: kagisearch fastfeedparser 0.5.10. Check the vendor advisory for mitigations.

References

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