# CVE-2026-126192: Soup Sieve: General sibling combinator inside :has() matches untrusted HTML in quadratic time

> Attacker-controlled HTML can cause quadratic processing time in apps evaluating fixed Soup Sieve selectors over untrusted markup.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **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
- **Fix available:** Yes
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-4j63-6c4x-wfg4

## What is CVE-2026-126192?

CVE-2026-126192 is a medium-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 2.10, matching a developer-authored selector that places the general sibling combinator inside :has() repeatedly scans each candidate element's following siblings when the right-hand side is absent, producing quadratic work on attacker-controlled HTML. Applications that evaluate a fixed selector such as div:has(a ~ b) over untrusted markup can have a worker occupied for minutes by a small document, while the adjacent sibling form and trusted-only document processing are not affected in the same way. This issue is fixed in version 2.10.

Weakness: CWE-407 (Inefficient Algorithmic Complexity), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-126192?

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

An affected version is only exploitable if your software uses the vulnerable function or option. Many projects that include it are not exposed.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `soupsieve` | PyPI | All versions | 2.10.0 |

## How do I fix CVE-2026-126192?

Upgrade soupsieve to 2.10.0 or later.

## Is CVE-2026-126192 being exploited?

There is no known exploitation of CVE-2026-126192 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126192 and fix it if it is affected.

What it is: CVE-2026-126192 is a medium-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-2026-126192 in the wild and no public exploit code.
Exposure: An affected version is only exploitable if your software uses the vulnerable function or option. Many projects that include it are not exposed.

Affected packages and fixed versions:
- soupsieve (PyPI): affected all versions; fixed in 2.10.0

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.
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-2026-126192/ (Markdown: https://insights.sbomify.com/CVE-2026-126192/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126192
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126192
- OSV: https://osv.dev/vulnerability/CVE-2026-126192

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126192/
Summaries are generated and may contain mistakes; the official description above is the record.