Bug 2536116 (CVE-2026-85999)

Summary:	CVE-2026-85999 soupsieve: Soup Sieve: Denial of Service via crafted CSS selectors
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
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
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. A remote attacker can provide a specially crafted CSS selector containing long whitespace or comment runs. This can cause excessive CPU consumption during selector trimming, leading to a Regular Expression Denial of Service (ReDoS) by stalling the service and exhausting system resources.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-17 15:53:07 UTC

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.9, selector_iter in src/soupsieve/css_parser.py trims the raw selector with RE_WS_END, an end-anchored WSC whitespace-and-comment expression used with search(), so the regular expression engine retries a greedy scan at every starting offset. An attacker-controlled valid selector containing a long internal whitespace run, or a selector containing a long CSS comment run followed by another token, causes quadratic CPU work before tokenization. User-controlled selectors can reach the path through soupsieve.compile() and BeautifulSoup.select(), while applications using only hard-coded selectors are unaffected. This root cause is separate from the IDENTIFIER and VALUE backtracking vulnerability because the cost occurs in RE_WS_END.search during trimming rather than token matching. The resulting CPU consumption can hold the Python GIL, exhaust workers, and stall a service without causing memory corruption or code execution. The issue is fixed in version 2.9.

Comment 1 Yadnyawalk Tale 2026-09-21 10:59:23 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