VulnerabilityPublished 13 Nov 2026

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

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-126190· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 0.23.1_3 soon.

Data as of 13 Nov 2026, 21:20 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 0.23.1_3

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

Upgrade mcp-atlassian to 0.23.1_3.

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.9 <0.23.1_3	Fixed in 0.23.1_3

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 Soup Sieve version 0.23.1_3 that fixes the vulnerability by implementing caching to reduce matching complexity. Users should upgrade to version 0.23.1_3 or later. No additional changes are required 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 selector operations with time limits in isolated processes. Avoid using the NOCACHE flag as it disables caching and reintroduces the vulnerability.

Description

Soup Sieve versions >=0.11.9 and <0.23.1_3 are vulnerable to a polynomial-time denial of service (DoS) caused by the descendant combinator in CSS selectors. The vulnerability arises because matching selectors with descendant combinators against deeply nested documents causes CPU time to grow polynomially with nesting depth, leading to significant processing delays. This can be exploited by an attacker controlling the HTML or XML input to cause high CPU usage and denial of service. The issue is fixed in version 0.23.1_3 by introducing caching to reduce matching time to linear complexity.

Impact

Applications using vulnerable versions of Soup Sieve that run CSS selectors with descendant combinators on untrusted or attacker-controlled HTML/XML documents can experience denial of service due to high CPU usage. This affects services such as scrapers, HTML sanitizers, filters, or any system processing uploaded or fetched markup. The vulnerability does not impact applications that only process trusted documents. The CVSS v3.1 score is 7.5 (high), reflecting network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability (denial of service).

Summary

The vulnerability in Soup Sieve involves the descendant combinator selector (e.g., 'a b'), where matching time grows polynomially with document nesting depth and the number of descendant combinators. Each additional descendant combinator increases the polynomial degree by one, resulting in O(n^(k+1)) time complexity for a selector with k descendant combinators on a chain of n nested elements. This inefficiency allows an attacker who controls the input document to craft a small but deeply nested structure that causes excessive CPU consumption during selector matching. The worst case occurs when the leftmost selector part never matches, forcing exhaustive ancestor walks. The issue is fixed in version 0.23.1_3 by caching match results per element and relation, reducing complexity to linear time.

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Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 21:20 UTC

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