CVE-2026-85999VulnerabilityPublished 20 Sep 2026Updated 29 Oct 2026

lexicon · Soup Sieve: Polynomial-time ReDoS (O(n²))

Affects lexiconSource GCVE Database

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Authoritative record:CVE-2026-85999· 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, 07:32 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 fix for this vulnerability is available in soupsieve version 3.25.2_3. Users should upgrade to this version or later to remediate the issue. Applications that do not accept user-controlled CSS selectors are not vulnerable. No additional mitigations are required once patched.

Description

A Regular Expression Denial of Service (ReDoS) vulnerability exists in soupsieve's whitespace/comment trimming regex RE_WS_END. The regex is used to trim trailing whitespace/comments from CSS selectors but is unanchored at the start and invoked with .search(), causing quadratic time complexity on valid selectors with long whitespace or comment runs. This can stall the interpreter for seconds on large inputs. The issue 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

The vulnerability causes a denial of service via excessive CPU consumption when processing valid CSS selectors containing long runs of whitespace or comments. This can stall applications using soupsieve or BeautifulSoup's selector APIs, potentially leading to performance degradation or unresponsiveness. There is no impact on confidentiality or integrity. Exploitation requires supplying crafted CSS selectors, so applications using only hard-coded selectors are not affected.

Summary

The vulnerability arises from the RE_WS_END regex in soupsieve's css_parser.py, which matches trailing whitespace/comments using an unanchored pattern with .search(). Because .search() tries every offset, and the pattern involves a greedy match followed by an end anchor, inputs with long whitespace or comment runs cause the regex engine to perform O(n²) work. This leads to significant CPU consumption and delays when compiling selectors containing large whitespace gaps or comment runs, even if the selectors are valid. The flaw is reproducible on soupsieve versions 2.8.4 and 2.9 and confirmed on Python 3.11.15 and 3.14.6. The issue is exploitable wherever user-controlled CSS selectors are passed to soupsieve or BeautifulSoup's select methods. The vulnerability is tracked as CVE-2026-85999 with a CVSS 3.1 score of 5.3 (medium severity). A patch fixing the issue is available in soupsieve version 3.25.2_3.

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Description

AI analysisMachine-generated, updated 30 Oct 2026, 07:32 UTC

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