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.
- 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
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.
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 | 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-126192 being exploited?
There is no known exploitation of CVE-2026-126192 in the wild and no public exploit code.
Sources
Also known as GHSA-4j63-6c4x-wfg4.