VulnerabilityPublished 13 Nov 2026

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

Affects favaSource 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 1.30.16_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 1.30.16_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 fava to 1.30.16_1.

Affected software

Product	Affected	Fixed in
Homebrewfava`pkg:brew/fava`Other threats	Affected >=1.14 <1.30.16_1	Fixed in 1.30.16_1

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

AI-suggested

A patch is available in version 1.30.16_1 of the affected product and should be applied to resolve this performance issue. Users should also avoid applying selectors with general sibling combinators inside :has() on untrusted HTML, especially when the anchor element has many children or when the inner selector is not tightly constrained. Using combinators like > or + inside :has() can reduce traversal and improve performance. Additionally, user input can be scanned to detect and deny selectors containing :has(), or selector evaluation can be wrapped in timeouts to prevent long-running processes. These mitigations reduce the risk of CPU exhaustion attacks.

Description

CVE-2026-126192 describes a performance-related vulnerability 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 arises because the implementation performs nested scans for each candidate element without short-circuiting when the right-hand side element is absent. This can be exploited to cause denial of service by stalling applications that run such selectors on attacker-controlled HTML. The vulnerability is mitigated by careful use of :has() selectors, limiting the scope of the anchor and inner selectors, and by applying patches available in version 1.30.16_1 of the affected product.

Impact

The vulnerability impacts availability by allowing an attacker to cause high CPU usage and stall the processing of HTML documents when a selector with a general sibling combinator inside :has() is evaluated against attacker-controlled markup. This can lead to denial of service conditions in applications that use Soup Sieve to parse and select elements from untrusted HTML. There is no indication of confidentiality or integrity impact. The issue is performance-related and can cause significant delays even on relatively small HTML inputs with thousands of sibling elements.

Summary

The vulnerability in Soup Sieve involves the use of a general sibling combinator (~) inside the :has() pseudo-class selector, e.g., div:has(a ~ b). When this selector is matched against untrusted HTML with many sibling elements, the matching process runs in O(n²) time due to nested scans for each candidate 'a' element checking for a following sibling 'b'. This quadratic time complexity can cause significant CPU consumption and stall applications processing such selectors. The adjacent sibling combinator (+) does not exhibit this issue as it only checks the immediate next sibling, maintaining linear time complexity. The problem is inherent to the design of :has() but can be optimized. The vulnerability affects versions >=1.14 and <1.30.16_1 of the product 'fava'. A fix is available in version 1.30.16_1. The CVSS 4.0 score is 6.3 (medium severity), reflecting the potential for partial availability impact via CPU exhaustion. Mitigations include avoiding broad or unconstrained use of :has() with general sibling combinators on untrusted input, using tighter combinators like > or +, scanning user input for risky selectors, and applying the official patch.

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Affected software

Description

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

Technical details

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