CVE-2026-126193VulnerabilityPublished 13 Nov 2026

soupsieve · Soup Sieve: Uncontrolled recursion

Affects soupsieveSource GCVE Database

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Authoritative record:CVE-2026-126193· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.0.2 when convenient.

Data as of 13 Nov 2026, 17:35 UTC

CVSS 3.1 base score

5.3Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	5.3

Patch: Available – fixed in 3.0.2

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 12 Nov 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 13 Nov 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 soupsieve to 3.0.2.

Affected software

Product	Affected	Fixed in
PyPIsoupsieve	Affected >=0.4 <3.0.2	Fixed in 3.0.2

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AI-suggested

A fix is available in Soup Sieve version 3.0.2. Users should upgrade to this version or later to prevent uncontrolled recursion in nested pseudo-class selectors. Until upgraded, applications should consider catching RecursionError exceptions when parsing selectors to handle this failure mode gracefully. No other mitigation is documented or required.

Description

Soup Sieve's CSS selector parser has an uncontrolled recursion vulnerability when parsing nested pseudo-class selectors such as :is(), :not(), :where(), and :has(). An attacker supplying a deeply nested selector string (about 330 levels) can cause a RecursionError by exceeding Python's recursion limit. This leads to a denial of service for the individual request or task parsing the selector. The issue affects versions from 0.4 up to but not including 3.0.2, with a fix available in 3.0.2. No confidentiality or integrity impact is present, and the failure occurs before document matching.

Impact

This vulnerability allows an attacker to cause a denial of service by triggering a RecursionError during CSS selector parsing, resulting in failure of the individual request or task that processes the malicious selector. There is no confidentiality or integrity impact. The error is recoverable and does not cause interpreter crashes or persistent resource exhaustion. Applications that do not handle RecursionError explicitly may experience unexpected failures when parsing untrusted selectors. The vulnerability requires no authentication or user interaction and affects any application exposing the relevant Soup Sieve or Beautiful Soup selector APIs to attacker-controlled input.

Summary

The Soup Sieve CSS selector parser recursively processes each nested pseudo-class selector without limiting recursion depth. This allows an unauthenticated attacker who can supply CSS selector strings to functions like soupsieve.compile(), soupsieve.select(), or Beautiful Soup's soup.select() / soup.select_one() to cause a RecursionError by crafting a selector with roughly 330 nested pseudo-class levels (about 1.6 KB). The parser's token-count guard does not limit recursion depth, so it does not prevent this. The RecursionError is not part of the documented error contract, so applications that only catch ValueError or SelectorSyntaxError will see unexpected failures. The impact is a transient denial of service on the parsing operation, not a crash or persistent resource exhaustion. The vulnerability affects Soup Sieve versions >=0.4 <3.0.2 and is fixed in version 3.0.2.

CWE-674Uncontrolled Recursion (opens in a new tab)
Class weakness
The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.
Implementation
Ensure that an end condition will be reached under all logic conditions. The end condition may include checking against the depth of recursion and exiting with an error if the recursion goes too deep. The complexity of the end condition contributes to the effectiveness of this action.
Implementation
Increase the stack size.
Attack patterns
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 17:35 UTC

WeaknessesCWE-674

Technical details

References

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