VulnerabilityPublished 13 Nov 2026

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

Affects dnsrobocertSource 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 3.27.1_1 or 3.24.1_1 when convenient.

Data as of 13 Nov 2026, 21:55 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 3.27.1_1, 3.24.1_1

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 dnsrobocert to 3.27.1_1 or 3.24.1_1.

Affected software

Product	Affected	Fixed in
Homebrewdnsrobocert`pkg:brew/dnsrobocert`Other threats	Affected >=3.24.1 <3.24.1_1 >=3.25.0 <3.27.1_1	Fixed in 3.24.1_1 3.27.1_1

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 versions 3.24.1_1 and 3.27.1_1 of the affected product. Users should upgrade to these versions to mitigate the issue. Additionally, developers should avoid using :has() with the general sibling combinator (~) on elements with many children or on untrusted HTML. Prefer using combinators like > or + inside :has() to limit traversal. If necessary, input containing :has() selectors can be scanned and rejected, or selector evaluation can be wrapped in timeouts to prevent long-running processes. The quadratic time behavior is expected in some cases and not a bug, so 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 when matched against untrusted HTML, causing potentially long CPU usage. The issue arises because the implementation performs nested scans for each candidate element, leading to O(n²) complexity. This can cause denial of service by stalling applications processing attacker-controlled HTML with such selectors. The vulnerability is mitigated by avoiding overly broad use of :has() with general sibling combinators and by applying patches available in fixed versions.

Impact

An attacker can cause high CPU usage and stall applications that evaluate selectors containing a general sibling combinator inside :has() over attacker-controlled HTML. This leads to denial of service by making the selector evaluation take minutes on relatively small HTML inputs with thousands of sibling elements. The impact is on availability, as the process is tied up in quadratic-time matching operations.

Summary

Soup Sieve's implementation of the :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 the right-hand sibling element is absent, the matching process performs nested scans over siblings, resulting in O(n²) operations. This can cause significant CPU consumption and stall processing for documents with thousands of sibling elements. The adjacent sibling combinator (+) does not exhibit this issue as it only checks the immediate next sibling, maintaining linear time. The vulnerability impacts availability by enabling denial of service through crafted HTML inputs. The issue is not a bug per se but a known performance characteristic of :has() with general sibling combinators. Fixed versions 3.24.1_1 and 3.27.1_1 address this problem by improving performance. Users are advised to limit the use of :has() with general sibling combinators on large or untrusted inputs and to prefer tighter combinators like > or + inside :has().

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Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:55 UTC

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