VulnerabilityPublished 13 Nov 2026

CVE-2026-126190: Soup Sieve · Polynomial-time denial of service in the descendant combinator

Affects gdownSource GCVE Database

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Authoritative record:CVE-2026-126190· High 7.5

Not known to be exploited · CVSS 7.5 High · fixed in 4.0 : patch gdown soon.

Data as of 13 Nov 2026, 21:55 UTC

CVSS 3.1 base score

7.5High

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 3.1	7.5

Patch: Available – fixed in 4.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 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
Homebrewgdown`pkg:brew/gdown`Other threats	Affected >=5.2.0	Fixed in–

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AI-suggested

A fix is available in Soup Sieve version 4.0, which introduces caching to reduce matching time to linear complexity. Users should upgrade to version 4.0 or later to mitigate this vulnerability. The caching mechanism is enabled by default and requires no code changes beyond upgrading. If upgrading is not possible, users should minimize the use of descendant combinators in selectors on untrusted input, limit the size and nesting depth of untrusted documents, or run selection operations with time limits in isolated worker processes. Avoid using the NOCACHE flag as it disables caching and reintroduces the vulnerability.

Description

CVE-2026-126190 is a denial of service vulnerability in Soup Sieve's handling of CSS selectors with descendant combinators. The matching algorithm exhibits polynomial-time complexity relative to the document's nesting depth and the number of descendant combinators, allowing an attacker controlling input HTML or XML to cause high CPU usage by crafting deeply nested documents. This can tie up application workers for extended periods. The issue is fixed in Soup Sieve version 4.0 by introducing caching to reduce matching time to linear complexity. Applications processing untrusted markup with descendant combinators in selectors are affected; those processing only trusted documents are not.

Impact

Applications using Soup Sieve to run CSS selectors with descendant combinators on untrusted HTML or XML documents can experience denial of service due to excessive CPU consumption. This can cause worker threads or processes to be tied up for extended durations (seconds to minutes) even with small input documents (~1 KB). The impact is limited to availability (denial of service) with no confidentiality or integrity effects. Applications that only process trusted documents are not affected.

Summary

Soup Sieve's selector matching for descendant combinators (e.g., 'a b') has a performance flaw where the time to match grows polynomially with document nesting depth and the number of descendant combinators in the selector. Each descendant combinator increases the exponent of the polynomial time complexity by one. The matching process repeatedly walks up ancestor chains without caching, causing repeated work. An attacker controlling the input markup can exploit this by submitting small but deeply nested documents, causing CPU usage to spike for seconds to minutes. The vulnerability affects selectors with descendant combinators run against untrusted documents. The issue was fixed in Soup Sieve 4.0 by caching match results per element and relation, reducing complexity to linear time. The fix is enabled by default and requires upgrading to version 4.0 or later.

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Exploitation evidence

What to do

Affected software

Description

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

Technical details

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