VulnerabilityPublished 13 Nov 2026

CVE-2026-126190: Soup Sieve · Polynomial-time denial of service in the descendant combinator

Affects lexiconSource GCVE Database

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Authoritative record:CVE-2026-126190· High 7.5

Not known to be exploited · CVSS 7.5 High · fixed in 4.0 : patch lexicon soon.

Data as of 13 Nov 2026, 21:19 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	7.5

Patch: Available – fixed in 4.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Homebrewlexicon`pkg:brew/lexicon`Other threats	Affected >=3.11.2	Fixed in–

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AI-suggested

Upgrade to Soup Sieve version 4.0 or later, where the vulnerability is fixed by caching intermediate match results. No code changes are required beyond upgrading. If upgrading is not possible, users should minimize the use of descendant combinators in selectors applied to untrusted documents, prefer child combinators ('a > b'), limit the size and nesting depth of untrusted input, and consider running selector operations with time limits or in isolated worker processes. Avoid using the NOCACHE flag as it disables the fix and reintroduces the vulnerability.

Description

Soup Sieve versions prior to 4.0 have a polynomial-time denial of service vulnerability in the descendant combinator selector processing. Matching selectors with descendant combinators against deeply nested documents causes CPU time to grow polynomially with nesting depth, allowing attackers controlling input HTML or XML to cause significant CPU consumption. This affects applications that run CSS selectors on untrusted markup. The issue is fixed in Soup Sieve 4.0 by caching intermediate results to ensure linear-time matching.

Impact

Applications that run descendant combinator selectors on untrusted HTML or XML documents can experience denial of service due to excessive CPU consumption. This can tie up worker processes for extended periods (seconds to minutes) with relatively small input documents (~1 KB). The vulnerability does not affect applications that only process trusted documents. There is no impact on confidentiality or integrity, only availability (denial of service).

Summary

Soup Sieve's selector engine suffers from a performance vulnerability when processing descendant combinators (e.g., 'a b'). The matching algorithm walks up the ancestor chain for each element without caching, causing time complexity to grow as O(n^(k+1)) for selectors with k descendant combinators on a chain of n nested elements. An attacker controlling input markup can exploit this by submitting a small but deeply nested document, causing CPU usage to spike for seconds or minutes. The worst case occurs when the leftmost selector part never matches, forcing full ancestor walks. This vulnerability affects versions >=3.11.2 and was fixed in version 4.0 by introducing caching of match results per element and relation, reducing complexity to linear time.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:19 UTC

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