VulnerabilityPublished 13 Nov 2026

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

Affects cloudsplainingSource GCVE Database

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Authoritative record:CVE-2026-126192· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium.

Data as of 13 Nov 2026, 21:32 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

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

Affected software

Product	Affected	Fixed in
Homebrewcloudsplaining`pkg:brew/cloudsplaining`Other threats	Affected >=0.6.2	Fixed in–

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AI-suggested

This quadratic time behavior is expected given the design of :has() with general sibling combinators and is not classified as a bug. Users should avoid applying :has() selectors with general sibling combinators on elements with large numbers of children, especially when processing untrusted HTML. Using more constrained combinators like adjacent sibling (+) or child (>) inside :has() can reduce traversal and improve performance. If the risk is unacceptable, input containing :has selectors can be rejected or selector evaluation wrapped in timeouts to prevent long-running processes. Future optimizations may improve performance but careful selector design is currently the best mitigation.

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 when evaluated against untrusted HTML, causing significant CPU delays. The issue arises because the implementation performs nested scans for each candidate element, leading to O(n²) complexity. This can stall applications processing attacker-controlled HTML. The vulnerability is related to algorithmic complexity rather than a traditional security flaw.

Impact

The impact is a denial of service condition due to high CPU consumption when evaluating selectors with a general sibling combinator inside :has() on untrusted HTML. An attacker can craft HTML with many sibling elements to cause the selector evaluation to take minutes of CPU time, effectively stalling the application. This affects availability but does not directly lead to code execution, data leakage, or privilege escalation.

Summary

Soup Sieve's implementation of the CSS :has() pseudo-class combined with the general sibling combinator (~) can cause quadratic time complexity when matching selectors like div:has(a ~ b) against untrusted HTML. Specifically, when no matching sibling 'b' is present, the algorithm performs nested scans over sibling elements, resulting in O(n²) comparisons. This leads to CPU usage that grows quadratically with the number of sibling elements, demonstrated by a proof of concept where processing thousands of sibling elements causes delays of several seconds to minutes. The adjacent sibling combinator (+) does not exhibit this issue as it only checks the immediate sibling, maintaining linear time. This behavior is inherent to the selector's design and not unique to Soup Sieve, but optimizations could reduce the impact. The vulnerability affects Soup Sieve versions >=0.6.2 and can cause denial of service by stalling processes that evaluate such selectors on attacker-controlled HTML.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:32 UTC

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