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.
CVE-2026-86000
This medium-severity CVE scores 5.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 62% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
- Lower severity and no public exploit yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.3
- EG Score
- 5.3(medium)
- EG Risk
- 55(Attend)EG Risk 55/100SSVC: Attend
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity53% × 45%Exploitation40% × 40%Automatability100% × 15%Action: Remediate soon — notable exploitation risk. - EPSS PROB
- 0%
- EPSS %ILE
- 38%
- KEV
- Not listed
Published
September 17, 2026
Last Modified
September 17, 2026
Advisory Details (3)
Auto-updated Sep 17, 20262.9
Patch available: facelessuser/soupsieve 2.9
https://github.com/facelessuser/soupsieve/releases/tag/2.9commit ce44e4996e66 (facelessuser/soupsieve)
Patch available: facelessuser/soupsieve 2.9 (contains commit ce44e4996e66)
https://github.com/facelessuser/soupsieve/commit/ce44e4996e6632871c18cdd7a7fb641be8ef34efPolynomial-time ReDoS (O(n²)) in the `IDENTIFIER` / `VALUE` selector sub-patterns · Advisory · facelessuser/soupsieve · GitHub
https://github.com/facelessuser/soupsieve/security/advisories/GHSA-gjv8-xp57-g29cVendor Advisories for CVE-2026-86000(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 6× in last 7d / 6× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-09-19 14:31 UTCEG score recompute
- 2026-09-18 19:28 UTCEPSS rescore
- 2026-09-17 17:57 UTCEG score recompute
- 2026-09-17 15:49 UTCEG score recompute
- 2026-09-17 15:35 UTCEG score recompute
- 2026-09-17 15:34 UTCMITRE cvelistV5first tracked
Frequently asked(5)
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Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-86000
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