Bug 2536121 (CVE-2026-86000)

Summary:	CVE-2026-86000 soupsieve: Soup Sieve: Denial of Service via crafted CSS selectors
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, anpicker, aos-team-art-private, aprice, asdas, bparees, cmyers, crizzo, dkeler, dnakabaa, doconnor, dpaolell, dschmidt, ebourniv, eglynn, hasun, jdelft, jfula, jjoyce, jlanda, jowilson, jpretori, jsamir, jschluet, jupierce, kaycoth, kshier, lcouzens, lgarciaa, lhh, mbiarnes, mburns, mgarciac, nyancey, oezr, ometelka, pakotvan, ppalepu, ppostler, prdhamdh, ptisnovs, rjohnson, sbunciak, sghai, sidsharm, simaishi, stcannon, sthirugn, suppawar, syedriko, teagle, thason, vlaad, xdharmai, yguenane, ytale
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in Soup Sieve, a CSS selector library. An attacker can craft a malicious CSS selector that, when processed by the library, leads to excessive CPU consumption. This occurs due to a polynomial-time regular expression denial of service (ReDoS) vulnerability in the selector parser. Successful exploitation can cause the application to stall, leading to a denial of service.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-17 15:53:32 UTC

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.

Comment 1 Yadnyawalk Tale 2026-09-21 11:08:38 UTC

CVSS Justification
====================

AV:N -> Since service accept a selector over HTTP/API, attack is network

AC:H -> In RH offerings, exploit needs an uncommon path that forwards untrusted CSS selectors into soupsieve; default hard-coded use is unaffected

PR:N -> No privileges assumed on that path; if only an authenticated admin UI ever accepted selectors, this would be PR:L instead

UI:N -> No second user interaction required

S:U -> DoS stays in the consuming process/component; no scope change

C:N -> No confidentiality impact; CPU exhaustion only

I:N -> No integrity impact; no data modification or code execution

A:H -> Successful hit can hold the Global Interpreter Lock, exhaust workers and stall the service - full/serious availability loss while the attack continues, not mild degradation