VulnerabilityPublished 20 Sep 2026Updated 29 Oct 2026

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

Affects lexiconSource GCVE Database

Compare

Authoritative record:CVE-2026-86000· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.25.2_3 when convenient.

Data as of 30 Oct 2026, 07:31 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 3.25.2_3

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 lexicon to 3.25.2_3.

Affected software

Product	Affected	Fixed in
Homebrewlexicon`pkg:brew/lexicon`Other threats	Affected >=3.11.2 <3.25.2_3	Fixed in 3.25.2_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 soupsieve version 3.25.2_3 that fixes this ReDoS vulnerability. Users should upgrade to this version or later. Applications that do not accept user-controlled CSS selectors are not affected. No other mitigation is required if the patch is applied.

Description

A Regular Expression Denial of Service (ReDoS) vulnerability exists in soupsieve's CSS selector parsing, specifically in the IDENTIFIER and VALUE sub-patterns. The flaw causes quadratic backtracking when parsing certain crafted selectors that fail to match, resulting in excessive CPU consumption. This can be triggered by user-controlled CSS selectors passed to soupsieve or BeautifulSoup's select methods. The vulnerability affects soupsieve versions from 3.11.2 up to but not including 3.25.2_3. A fix is available in version 3.25.2_3.

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 parser. This results in high CPU usage and significant delays in processing selectors, potentially stalling applications that use soupsieve or BeautifulSoup's select functions with user-controlled input. There is no impact on confidentiality or integrity, only availability is affected.

Summary

Soupsieve compiles CSS selectors using hand-written regex patterns. The IDENTIFIER sub-pattern and the embedded VALUE pattern contain adjacent quantified groups over overlapping character classes, leading to O(n²) regex backtracking on failing matches. This occurs when a selector includes a long identifier or attribute value run that ultimately fails to match, such as an unterminated attribute value or an invalid trailing character. The vulnerability is exploitable when user-controlled selectors are passed to soupsieve.compile() or BeautifulSoup's select methods. Performance measurements show that selector strings of a few thousand characters can stall the interpreter for seconds, with longer inputs causing minutes of CPU time. The issue is confirmed in soupsieve 2.8.4 and persists through versions >=3.11.2 <3.25.2_3. The problem is fixed in version 3.25.2_3.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 07:31 UTC

Technical details

References

Community reviews

Related threats