Vulnerability · Published Sep 17, 2026 · Assigned by GitHub_M
CVE-2026-86000Soup Sieve: Polynomial-time ReDoS (O(n²)) in the `IDENTIFIER` / `VALUE` selector sub-patterns
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in soupsieve from facelessuser. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.9, the selector parser in src/soupsieve/css_parser.py defines IDENTIFIER with adjacent quantified groups over overlapping character classes, and VALUE embeds IDENTIFIER for attribute selectors. When an attacker-controlled selector contains a long identifier or unquoted attribute-value run followed by input that makes the overall match fail, the regular expression engine explores quadratically many splits between the overlapping groups. User-controlled selectors can reach this path through soupsieve.compile(), soupsieve.select(), or BeautifulSoup.select(), while applications using only hard-coded selectors are unaffected. The resulting CPU consumption can hold the Python GIL, exhaust application workers, and stall a service; successful plain identifier matches are linear, and the issue does not cause memory corruption or code execution. The issue is fixed in version 2.9.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | soupsieve | no fix listed | DEBIAN-CVE-2026-86000 |
| Debian:13 | soupsieve | no fix listed | DEBIAN-CVE-2026-86000 |
| Debian:14 | soupsieve | no fix listed | DEBIAN-CVE-2026-86000 |
| PyPI | soupsieve | 2.9.0 | GHSA-gjv8-xp57-g29c |
| PyPI | soupsieve | 2.9.0 | PYSEC-2026-4170 |
| Ubuntu:22.04:LTS | soupsieve | no fix listed | UBUNTU-CVE-2026-86000 |
| Ubuntu:24.04:LTS | soupsieve | no fix listed | UBUNTU-CVE-2026-86000 |
| Ubuntu:26.04:LTS | soupsieve | no fix listed | UBUNTU-CVE-2026-86000 |
| Ubuntu:26.10 | soupsieve | no fix listed | UBUNTU-CVE-2026-86000 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| facelessuser | soupsieve | < 2.9 |
Weakness: CWE-400, CWE-1333 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L