# Soup Sieve: Regular Expression Denial of Service (ReDoS) via Selector Parser

Advisory record · `GHSA-836r-79rf-4m37`

- **Identifiers:** `GHSA-836r-79rf-4m37` · `CVE-2026-49477` · `PYSEC-2026-3072`
- **State:** Confirmed
- **Severity:** CVSS 7.5 High
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-1333](https://cwe.mitre.org/data/definitions/1333.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 9 Jul 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 9 Jul 2026, 13:37 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `soupsieve` (PyPI): affected `<2.8.4`; fixed in `2.8.4`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Soupsieve versions before 2.8.4 are vulnerable to regular expression denial of service through the CSS selector parser. An attacker who can supply a CSS selector string, such as an unterminated quoted attribute value, can make the parser consume CPU for seconds with a payload of about 300 bytes, which can block application threads. Upgrade to soupsieve 2.8.4 or later. No other workaround is listed.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 7.5 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0064, the 51st percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:11 UTC: First seen by agentprime
- 31 Oct 2026, 14:11 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-836r-79rf-4m37)

## Sources

- [GitHub Advisory Database: GHSA-836r-79rf-4m37](https://github.com/advisories/GHSA-836r-79rf-4m37)
- [OSV: GHSA-836r-79rf-4m37](https://osv.dev/vulnerability/GHSA-836r-79rf-4m37)
- <https://github.com/facelessuser/soupsieve/security/advisories/GHSA-836r-79rf-4m37>
- <https://github.com/facelessuser/soupsieve>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-836r-79rf-4m37>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-836r-79rf-4m37/>. Everything for agents: <https://agentprime.io/llms.txt>.