VulnerabilityPublished 13 Nov 2026

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

Affects aqtinstallSource 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 3.3.0_11 when convenient.

Data as of 13 Nov 2026, 21:33 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 3.3.0_11

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 aqtinstall to 3.3.0_11.

Affected software

Product	Affected	Fixed in
Homebrewaqtinstall`pkg:brew/aqtinstall`Other threats	Affected >=3.2.0 <3.3.0_11	Fixed in 3.3.0_11

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AI-suggested

A patch is available in version 3.3.0_11 of aqtinstall that addresses this issue. Users should upgrade to this version or later. The vendor notes that quadratic time complexity for :has() in some cases is expected due to selector semantics, so users should apply :has() selectors thoughtfully. Specifically, avoid using :has() with general sibling combinators (~) on elements with many children or untrusted input. Use more constrained combinators like > or + inside :has() to limit traversal. Additionally, scanning user input for :has usage and denying such input or wrapping selector evaluation calls in timeouts can mitigate risk. If the risk is unacceptable, avoid running selectors with :has() on untrusted HTML.

Description

CVE-2026-126192 describes a performance issue in Soup Sieve when using the CSS selector pattern with a general sibling combinator inside :has(), such as div:has(a ~ b). This pattern causes the selector matching to run in quadratic time relative to the number of sibling elements, leading to potentially long CPU processing times on untrusted HTML inputs. The issue is due to nested scanning of siblings when the right-hand side element is absent, causing O(n²) complexity. This can be exploited to cause denial of service by stalling applications that run such selectors on attacker-controlled HTML. The vulnerability affects versions >=3.2.0 and <3.3.0_11 of the product aqtinstall. A fix is available in version 3.3.0_11. The vendor advises careful use of :has() selectors and suggests mitigation strategies including limiting the use of general sibling combinators and applying timeouts or input scanning to prevent abuse.

Impact

The vulnerability impacts availability by allowing an attacker to cause excessive CPU consumption when an application evaluates a selector containing a general sibling combinator inside :has() over attacker-controlled HTML. This can stall the process for minutes on relatively small HTML inputs, effectively causing a denial of service. The issue arises from the quadratic time complexity of the selector matching algorithm in this scenario. There is no indication of confidentiality or integrity impact.

Summary

Soup Sieve's implementation of the CSS :has() pseudo-class combined with the general sibling combinator (~) can cause selector matching to execute in O(n²) time when applied to untrusted HTML with many sibling elements. Specifically, selectors like div:has(a ~ b) require nested scans of siblings to determine if an element contains an 'a' followed by a sibling 'b'. When 'b' is absent, the algorithm cannot short-circuit and performs a quadratic number of comparisons, resulting in significant CPU usage. This behavior is inherent to the selector semantics but can be optimized. The vulnerability allows an attacker controlling HTML input to cause denial of service by forcing long processing times. The issue affects aqtinstall versions >=3.2.0 and <3.3.0_11, with a fix available in 3.3.0_11. The vendor recommends cautious use of :has() with general sibling combinators and suggests mitigation such as restricting selectors and applying timeouts.

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Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:33 UTC

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