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

> An attacker can cause CPU exhaustion and denial of service by supplying malicious CSS selector strings to the soupsieve library.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Jul 2026
- **Updated:** 21 Jul 2026
- **Also known as:** CLEANSTART-2026-DI63885, DEBIAN-CVE-2026-49477, ECHO-a29a-2b91-4618, GHSA-836r-79rf-4m37, MINI-5f4f-5wj2-954v, MINI-5pfr-qxr9-8qxw, MINI-79mj-2544-q8fc, MINI-8jcw-m5jc-f8jq, MINI-gg9p-72hr-vcx3, MINI-mv5x-g7x5-mw36, PYSEC-2026-3072, ROOT-APP-PYPI-CVE-2026-49477, UBUNTU-CVE-2026-49477

## What is CVE-2026-49477?

CVE-2026-49477 is a high-severity denial of service vulnerability in facelessuser soupsieve, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-400 (Uncontrolled Resource Consumption), CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-49477?

3 open source packages ship an affected version, including soupsieve. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `soupsieve` | PyPI | All versions | 2.8.4 |
| `soupsieve` | PyPI | All versions | 2.8.4 |
| `soupsieve` | PyPI | All versions | 2.8.4 |

Products: Facelessuser Soup Sieve.

## How do I fix CVE-2026-49477?

Upgrade soupsieve to 2.8.4 or later.

## Is CVE-2026-49477 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49477 exists.

## Other vulnerabilities in facelessuser soupsieve

- [CVE-2026-49476](https://insights.sbomify.com/CVE-2026-49476/): Soup Sieve: Memory Exhaustion via Large Comma-Separated Selector Lists in soupsieve (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49477 and fix it if it is affected.

What it is: CVE-2026-49477 is a high-severity denial of service vulnerability in facelessuser soupsieve, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49477 exists.

Affected packages and fixed versions:
- soupsieve (PyPI): affected all versions; fixed in 2.8.4
- soupsieve (PyPI): affected all versions; fixed in 2.8.4
- soupsieve (PyPI): affected all versions; fixed in 2.8.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49477/ (Markdown: https://insights.sbomify.com/CVE-2026-49477/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49477
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49477
- OSV: https://osv.dev/vulnerability/CVE-2026-49477

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49477/
Summaries are generated and may contain mistakes; the official description above is the record.