VulnerabilityPublished 18 Sep 2026Updated 29 Oct 2026

CVE-2026-86000: Soup Sieve · Polynomial-time ReDoS (O(n²)) in the `IDENTIFIER` / `VALUE` selector sub-patterns

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-86000· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 0.23.1 when convenient.

Data as of 30 Oct 2026, 08:15 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 0.23.1

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

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

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: 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 impacted component 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 impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Sep 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 29 Oct 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.

Affected software

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

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 soupsieve version 0.23.1 that fixes the regex backtracking issue. Users and applications relying on soupsieve or BeautifulSoup with user-supplied selectors should upgrade to version 0.23.1 or later. If upgrading is not immediately possible, avoid passing user-controlled input directly to soupsieve or BeautifulSoup select methods to prevent exploitation.

Description

A Regular Expression Denial of Service (ReDoS) vulnerability exists in soupsieve's CSS selector parsing due to a quadratic-time regex backtracking issue in the IDENTIFIER and VALUE sub-patterns. This flaw can cause the interpreter to stall for seconds or minutes when processing crafted selectors with long identifier or attribute value runs that fail to match. The vulnerability is exploitable when user-controlled selectors are passed to soupsieve or BeautifulSoup's select methods. It affects soupsieve versions from 0.11.9 up to but not including 0.23.1. A fix is available in version 0.23.1.

Impact

An attacker can cause a denial of service by supplying a specially crafted CSS selector string that triggers quadratic regex backtracking in soupsieve's parsing logic. This leads to high CPU usage and significant delays in processing, effectively stalling applications that use soupsieve or BeautifulSoup's select methods with user-controlled selectors. There is no direct impact on confidentiality or integrity, only availability due to resource exhaustion.

Summary

Soupsieve compiles CSS selectors using hand-written regex patterns where the IDENTIFIER sub-pattern contains adjacent quantified groups over overlapping character classes, causing quadratic backtracking on failing matches. Specifically, the pattern uses a construct like (?:C)+(?:C)* where C is an overlapping character class, leading to O(n²) parse time when the selector string is crafted to fail (e.g., unterminated attribute values or invalid trailing characters). This results in significant CPU consumption and interpreter stalls for selectors of a few kilobytes or more. The vulnerability is reachable via soupsieve's compile and select functions, including BeautifulSoup's select methods, if user input is passed as selectors. The issue is confirmed in soupsieve versions >=0.11.9 and <0.23.1 and fixed in 0.23.1.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:15 UTC

Technical details

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