# CVE-2026-126190: Soup Sieve: Polynomial-time denial of service in the descendant combinator

> Deeply nested attacker-influenced HTML or XML can make selector matching consume excessive CPU in applications using Soup Sieve on untrusted documents.

- **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
- **Harmful if only installed:** No
- **Needs a specific call:** Yes (`select()`, `select_one()`)
- **Fix available:** Yes
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-mmhr-3c5m-f64f

## What is CVE-2026-126190?

CVE-2026-126190 is a high-severity denial of service vulnerability in facelessuser soupsieve, published on 12 Nov 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 4.0, Soup Sieve repeatedly walks the same ancestors while matching descendant combinators, and each additional descendant combinator raises the polynomial degree of the work on deeply nested attacker-influenced HTML or XML. Applications using selectors such as section div div through select(), select_one(), or Beautiful Soup CSS APIs against untrusted documents can have a worker occupied for seconds or minutes, while trusted-only document processing is not affected. Selectors compiled with NOCACHE continue to use the old uncached behavior. This issue is fixed in version 4.0.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-126190?

1 open source package ship an affected version, including soupsieve.

An affected version is only exploitable if your software calls select() or select_one(). Many projects that include it are not exposed.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `soupsieve` | PyPI | All versions | 4.0.0 |

## How do I fix CVE-2026-126190?

Upgrade soupsieve to 4.0.0 or later.

## Is CVE-2026-126190 being exploited?

There is no known exploitation of CVE-2026-126190 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126190 and fix it if it is affected.

What it is: CVE-2026-126190 is a high-severity denial of service vulnerability in facelessuser soupsieve, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-126190 in the wild and no public exploit code.
Exposure: An affected version is only exploitable if your software calls select() or select_one(). Many projects that include it are not exposed.

Affected packages and fixed versions:
- soupsieve (PyPI): affected all versions; fixed in 4.0.0

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.
   If an affected version is present, also search the code for calls to select() or select_one() and report whether any exist.
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-2026-126190/ (Markdown: https://insights.sbomify.com/CVE-2026-126190/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126190
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126190
- OSV: https://osv.dev/vulnerability/CVE-2026-126190

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126190/
Summaries are generated and may contain mistakes; the official description above is the record.