Request: PYSEC ID for feedparser <= 6.0.11 (ReDoS in _sync_author_detail(), CWE-1333)

[kmanan]

Request

Requesting a PYSEC ID and CVE assignment for a confirmed ReDoS vulnerability in the feedparser package (PyPI). Maintainer is unresponsive after 64+ days.

Summary

• Package: feedparser (PyPI)
• Affected: <= 6.0.11; also confirmed present in 6.0.12 development branch (current main, last pushed 2026-05-11)
• Class: CWE-1333 (Inefficient Regular Expression Complexity), CWE-400 (Uncontrolled Resource Consumption)
• CVSS v3.1: 7.5 — AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Location: feedparser/mixin.py lines 42-43 (regex constant), used in _sync_author_detail() at line 783

Vulnerable pattern

# feedparser/mixin.py:42-43 (current main)
r"(([a-zA-Z0-9_.+-]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)"
r"|(([a-zA-Z0-9-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(]?))"

The sub-pattern (([a-zA-Z0-9-]+\.)+) is a nested quantifier of the form (X+)+. When a crafted <author> element forces the trailing TLD group to fail, the engine backtracks through all partitions of the dotted segments, producing super-linear time complexity.

Impact

An attacker hosting a malicious RSS/Atom feed can cause CPU exhaustion in any application calling feedparser.parse(feed_url). Multiple <item> elements linearly amplify the impact. Affected use cases: self-hosted RSS readers, news aggregators, and any backend that ingests user-submitted or third-party feed URLs.

Proof of Concept

Public repository with a five-part validation (isolated regex, integration, multi-item amplification, payload variants, safe-regex comparison):

https://github.com/kmanan/feedparser-redos-poc

Run:

pip install feedparser
git clone https://github.com/kmanan/feedparser-redos-poc
cd feedparser-redos-poc
python feedparser_redos_poc.py

Built-in safety stops cap individual tests at 30-60 seconds.

Proposed fix

# Vulnerable:
r"(([a-zA-Z0-9-]+\.)+)"

# Fixed:
r"([a-zA-Z0-9-.]+)"

Both accept the same valid email-domain inputs. The flat form has no nested quantifier and cannot exhibit catastrophic backtracking.

Disclosure timeline

Date	Event
2026-03-09	Maintainer (Kurt McKee) notified privately
2026-03-16	Reported to Snyk
2026-04-19	Public disclosure at kurtmckee/feedparser#562 after 41 days of maintainer silence
2026-05-12	No maintainer response. Repository remains actively committed to (last push 2026-05-11).

A second independent researcher (@jacopotediosi) has reported separate XSS vulnerabilities to the same maintainer with the same outcome — no response. Pattern of unresponsiveness across at least two independent reports.

Draft OSV YAML

id: PYSEC-0000-0000
details: |
  feedparser versions <= 6.0.11 (and the 6.0.12 development branch as of
  2026-05) contain a Regular Expression Denial of Service (ReDoS)
  vulnerability in the email regex defined at `feedparser/mixin.py` lines
  42-43 and used in `_sync_author_detail()` at line 783.

  The regex contains the sub-pattern `(([a-zA-Z0-9-]+\.)+)`, a nested
  quantifier of the form `(X+)+`. When a crafted `<author>` element forces
  the trailing TLD group to fail to match, the engine backtracks through all
  partitions of the dotted segments, producing super-linear time complexity.

  An attacker hosting a malicious RSS/Atom feed can cause CPU exhaustion in
  any application calling `feedparser.parse(feed_url)`. Multiple `<item>`
  elements linearly amplify the impact.

  Proof of concept: https://github.com/kmanan/feedparser-redos-poc

  Proposed fix: replace the nested quantifier `(([a-zA-Z0-9-]+\.)+)` with a
  flat character class `([a-zA-Z0-9-.]+)`.
aliases: []
modified: "2026-05-12T00:00:00Z"
published: "2026-05-12T00:00:00Z"
affected:
  - package:
      name: feedparser
      ecosystem: PyPI
      purl: pkg:pypi/feedparser
    ranges:
      - type: ECOSYSTEM
        events:
          - introduced: "0"
    versions:
      - "6.0.11"
    database_specific:
      cwe_ids:
        - CWE-1333
        - CWE-400
references:
  - type: REPORT
    url: https://github.com/kurtmckee/feedparser/issues/562
  - type: EVIDENCE
    url: https://github.com/kmanan/feedparser-redos-poc
  - type: PACKAGE
    url: https://pypi.org/project/feedparser/
credits:
  - name: Manan Kakkar
    type: REPORTER
    contact:
      - https://github.com/kmanan

Happy to open a PR adding this YAML under vulns/feedparser/ if that's the preferred submission flow.

References

• Upstream public disclosure: ReDoS vulnerability in email regex in mixin.py (feedparser ≤ 6.0.11) kurtmckee/feedparser#562
• PoC repository: https://github.com/kmanan/feedparser-redos-poc
• PyPI package: https://pypi.org/project/feedparser/

Credit

Reporter: Manan Kakkar (@kmanan)