CVE-2026-85999VulnerabilityPublished 18 Sep 2026Updated 27 Oct 2026

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

Affects pferdSource GCVE Database

Authoritative record:CVE-2026-85999· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.9.3 when convenient.

Data as of 27 Oct 2026, 23:14 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 3.9.3

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
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 pferd to 3.9.3.

Affected software

Product	Affected	Fixed in
Homebrewpferd`pkg:brew/pferd`Other threats	Affected >=3.4.2 <3.9.3	Fixed in 3.9.3

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

AI-suggested

A fix is available in soupsieve version 3.9.3. Users should upgrade to version 3.9.3 or later to resolve this vulnerability. Applications that do not accept user-controlled selectors are not affected. No other mitigation is required.

Description

A Regular Expression Denial of Service (ReDoS) vulnerability exists in soupsieve's whitespace/comment trimming regex `RE_WS_END`. The regex is used unanchored with `.search()`, causing quadratic time complexity (O(n²)) on valid CSS selectors with long whitespace or comment runs. This can stall the interpreter for seconds on large inputs. The issue affects soupsieve versions from 3.4.2 up to but not including 3.9.3 and is fixed in 3.9.3.

Impact

An attacker can supply a specially crafted but valid CSS selector string containing a long run of whitespace or comments to cause the soupsieve selector compiler to consume excessive CPU time, resulting in denial of service by stalling the interpreter. This affects applications that accept user-controlled CSS selectors and use soupsieve or BeautifulSoup's select APIs. There is no impact on confidentiality or integrity, only availability (denial of service).

Summary

Soupsieve's selector tokenizer trims trailing whitespace/comments using the regex `RE_WS_END = re.compile(r'{WSC}*$')` applied with `.search()`. Because this regex is only anchored at the end and not the start, `.search()` attempts matching at every offset in the input string. When the input contains a long run of whitespace or CSS comments not exactly at the end, the regex engine performs greedy matching and backtracking repeatedly, resulting in O(n²) time complexity. This triggers on valid selectors such as a descendant combinator with a large whitespace gap (e.g., 'a' + many spaces + 'b'). The vulnerability is reproducible on soupsieve versions 2.8.4 and HEAD 2.9, and confirmed on Python 3.11 and 3.14. The issue is fixed in soupsieve 3.9.3.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 23:14 UTC

Technical details

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