VulnerabilityPublished 20 Sep 2026Updated 26 Oct 2026

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

Affects flexgetSource GCVE Database

Authoritative record:CVE-2026-86000· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.19.30 when convenient.

Data as of 26 Oct 2026, 17:27 UTC

CVSS 3.1 base score

5.3Medium

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

EPSS: 0.6% chance of exploitation in 30 days – higher than 48% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.19.30

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
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 flexget to 3.19.30.

Affected software

Product	Affected	Fixed in
Homebrewflexget`pkg:brew/flexget`Other threats	Affected >=3.17.7 <3.19.30	Fixed in 3.19.30

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 version 3.19.30 of the affected product. Users should upgrade to this version or later to remediate the vulnerability. Applications that do not accept user-controlled CSS selectors are not affected. No additional mitigations are 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-time regex backtracking when parsing certain crafted selectors that fail to match, such as unterminated attribute values or identifiers followed by invalid characters. This can stall the interpreter for seconds to 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 version 3.19.30 of the affected product.

Impact

An attacker can supply a specially crafted CSS selector string that causes soupsieve's regex engine to perform excessive backtracking, resulting in a denial of service by stalling the interpreter for extended periods. This impacts availability but does not affect confidentiality or integrity. The vulnerability requires user-controlled input to the selector parsing functions and does not affect applications using only hard-coded selectors.

Summary

Soupsieve uses hand-written regex patterns to compile CSS selectors. The IDENTIFIER sub-pattern contains two adjacent quantified groups over overlapping character classes, causing O(n²) backtracking on failing matches. This occurs when a selector includes a long run of characters that ultimately fail to match, such as an unterminated attribute value or an invalid trailing character. The quadratic backtracking leads to significant CPU consumption and delays. The vulnerability is triggered via soupsieve.compile() and related APIs, including BeautifulSoup's select methods when user input is used as selectors. The issue is reproducible on soupsieve 2.8.4 and HEAD 2.9, and affects flexget versions >=3.17.7 and <3.19.30. A fix is available in version 3.19.30.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 17:27 UTC

Technical details

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