CVE-2026-39376 json
FastFeedParser has an infinite redirect loop DoS via meta-refresh chain
published 2026-04-07 7 mo ago modified 2026-07-24 3 mo ago also GHSA-4gx2-pc4f-wq37 , PYSEC-2026-60 , EUVD-2026-19915
- cvss
- 7.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 27%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- pypi fastfeedparser 0.5.10
- kagi fastfeedparser 0.5.10
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 7 mo ago
Exploit prediction
0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/kagisearch/fastfeedparser/security/advisories/GHSA-4gx2-pc4f-wq37 referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| GitHub | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| OSV | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | fastfeedparser | <0.5.10 |
0.5.10 |
Affected products
- kagisearch fastfeedparser
Classification
References
-
github.com
/kagisearch/fastfeedparser/security/advisories/GHSA-4gx2-pc4f-wq37
exploit, web, vendor-advisory, evidence
-
nvd.nist.gov
/vuln/detail/CVE-2026-39376
advisory
-
github.com
/kagisearch/fastfeedparser
package
-
github.com
/pypa/advisory-database/tree/main/vulns/fastfeedparser/PYSEC-2026-60.yaml
web
Sources
- CVE List CVE-2026-39376
- GitHub Advisory GHSA-4gx2-pc4f-wq37
- NVD CVE-2026-39376
- OSV PYSEC-2026-60
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