VulnerabilityPublished 13 Nov 2026

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

Affects pferdSource 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 pferd soon.

Data as of 13 Nov 2026, 21:05 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
Homebrewpferd`pkg:brew/pferd`Other threats	Affected >=3.4.2	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 matching results. No code changes are needed beyond upgrading. If upgrading is not possible, reduce the use of descendant combinators in selectors on untrusted input, limit the size and nesting depth of untrusted documents before selection, or run selection with a time limit in a stoppable worker process. Avoid using selectors compiled with the NOCACHE flag on untrusted input, as they remain vulnerable.

Description

Soup Sieve versions prior to 4.0 have a polynomial-time denial of service vulnerability in the descendant combinator selector matching. The time to match selectors with descendant combinators grows polynomially with document nesting depth, causing high CPU usage on deeply nested untrusted documents. This can lead to denial of service by tying up processing resources for seconds to minutes. The issue is fixed in version 4.0 by caching intermediate results to achieve linear time complexity.

Impact

Applications that run CSS selectors with descendant combinators on untrusted HTML or XML documents using affected Soup Sieve versions can experience denial of service due to excessive CPU usage. This can cause worker processes to be tied up for extended periods (seconds to minutes) even with small (around 1 KB) but deeply nested documents. Services such as scrapers, HTML sanitizers, or filters that process untrusted markup are vulnerable. Applications processing only trusted documents are not affected.

Summary

Soup Sieve's selector matching for descendant combinators (e.g., 'a b') is vulnerable to a polynomial-time denial of service attack. Matching a selector with k descendant combinators takes O(n^(k+1)) time on a chain of n nested elements, due to repeated ancestor walks without caching. An attacker controlling input HTML or XML can craft deeply nested documents that cause excessive CPU consumption when selectors with descendant combinators are run. The worst case occurs when the leftmost selector part never matches, forcing full ancestor walks. This vulnerability affects applications using Soup Sieve or Beautiful Soup's select methods on untrusted markup. The issue is fixed in Soup Sieve 4.0 by caching match results per element and relation, reducing complexity to linear time. The fix is enabled by default and requires upgrading to version 4.0 or later.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:05 UTC

Technical details

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