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 jupyterlabSource 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 4.6.2 when convenient.

Data as of 30 Oct 2026, 08:59 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 4.6.2

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 jupyterlab to 4.6.2.

Affected software

Product	Affected	Fixed in
Homebrewjupyterlab`pkg:brew/jupyterlab`Other threats	Affected >=3.3.2 <4.6.2	Fixed in 4.6.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in soupsieve version 4.6.2. Users should upgrade to this version or later to remediate the vulnerability. If upgrading is not immediately possible, avoid passing user-controlled CSS selectors to soupsieve or BeautifulSoup's select methods. No other specific mitigations are indicated by the vendor advisory.

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 arises from overlapping quantified character classes causing quadratic backtracking when parsing long, malformed selectors that fail to match. This can cause the interpreter to stall for seconds or minutes depending on input size. The vulnerability is exploitable when user-controlled CSS selectors are passed to soupsieve or BeautifulSoup's select methods. Fixed in soupsieve version 4.6.2.

Impact

An attacker can supply a specially crafted CSS selector string that triggers quadratic regex backtracking, causing the parsing process to consume excessive CPU time and stall the interpreter. This results in a denial of service (DoS) condition affecting availability. There is no impact on confidentiality or integrity. Exploitation requires the application to accept user-controlled selectors, which is common in scrapers, no-code extraction tools, or admin/query interfaces. Hard-coded selectors are not vulnerable.

Summary

Soupsieve compiles CSS selectors using hand-written regex patterns. The IDENTIFIER sub-pattern uses two adjacent quantified groups over overlapping character classes, leading to O(n²) regex backtracking on failing matches. This occurs when selectors contain long runs of identifier characters that do not match due to syntax errors (e.g., unterminated attribute values). The quadratic backtracking causes significant CPU delays, demonstrated by multi-second stalls on inputs of a few thousand characters. The vulnerability affects any application passing user-controlled selectors to soupsieve or BeautifulSoup's select functions. The issue is fixed in soupsieve 4.6.2.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:59 UTC

Technical details

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