VulnerabilityPublished 13 Nov 2026

CVE-2026-126192: Soup Sieve · General sibling combinator inside :has() matches untrusted HTML in quadratic time

Affects lexiconSource GCVE Database

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Authoritative record:CVE-2026-126192· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium : upgrade to 3.25.2_4 when convenient.

Data as of 13 Nov 2026, 21:21 UTC

CVSS 4.0 base score

6.3Medium

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 4.0	6.3

Patch: Available – fixed in 3.25.2_4

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 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

Upgrade lexicon to 3.25.2_4.

Affected software

Product	Affected	Fixed in
Homebrewlexicon`pkg:brew/lexicon`Other threats	Affected >=3.11.2 <3.25.2_4	Fixed in 3.25.2_4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Soup Sieve version 3.25.2_4. Users should upgrade to this version or later to benefit from performance improvements. Additionally, users should avoid running selectors with general sibling combinators inside :has() on untrusted or attacker-controlled HTML. Selector design should limit the number of children of the anchor element and use combinators like > or + inside :has() to reduce traversal. If risk remains, input containing :has() selectors can be blocked or calls wrapped in timeouts to prevent long-running evaluations. These mitigations align with the vendor's advisory that quadratic time behavior is expected in some cases and careful use of :has() is recommended.

Description

CVE-2026-126192 describes a performance issue in Soup Sieve when using a CSS selector with a general sibling combinator inside :has(), such as div:has(a ~ b). This selector runs in quadratic time relative to the number of sibling elements, causing significant CPU consumption and potential denial of service when processing untrusted HTML. The issue arises because the selector engine performs nested scans for each candidate element, leading to O(n²) complexity. This behavior is inherent to the design of :has() with general sibling combinators and is not classified as a bug but a known performance characteristic. A fix is available in version 3.25.2_4, which improves performance. Users are advised to limit the use of :has() with general sibling combinators on untrusted input and consider timeouts or input filtering to mitigate risk.

Impact

The impact is a denial of service via resource exhaustion (CPU time) when an application uses a selector with a general sibling combinator inside :has() on untrusted HTML input. This can cause the selector evaluation to take minutes on relatively small HTML fragments with a few thousand sibling elements, leading to application stalls or degraded availability. There is no direct compromise of confidentiality or integrity reported. The vulnerability is rated medium severity with a CVSS 4.0 score of 6.3.

Summary

The vulnerability CVE-2026-126192 affects Soup Sieve versions >=3.11.2 and <3.25.2_4. It involves the use of a CSS selector with a general sibling combinator (~) inside the :has() pseudo-class, for example div:has(a ~ b). When this selector is matched against untrusted HTML containing many sibling elements, the evaluation runs in O(n²) time due to nested scanning of siblings for each candidate element. This can cause the process to consume excessive CPU time (minutes for a few thousand siblings), effectively stalling applications that run such selectors on attacker-controlled markup. The adjacent sibling combinator (+) does not exhibit this issue as it runs in linear time. The root cause is the inability to short-circuit the search when the right-hand sibling is absent, leading to repeated scanning. Although this is a known performance limitation of :has() with general sibling combinators, Soup Sieve has implemented optimizations and a fix is available in version 3.25.2_4. Mitigations include careful selector design to limit the scope and complexity of :has(), avoiding anchors with many children, and restricting combinators inside :has() to those with better performance characteristics.

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Affected software

Description

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

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