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

> A malicious page can execute arbitrary JavaScript in Firefox for iOS Reader View due to incorrect HTML replacement order.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 1 Jun 2026
- **Updated:** 1 Jun 2026
- **Also known as:** GHSA-h55j-6jm9-f8vp

## What is CVE-2026-9308?

CVE-2026-9308 is a medium-severity cross-site scripting vulnerability in Mozilla Firefox, published on 1 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-9308?

It affects 1 product.


Products: Mozilla Firefox.

## How do I fix CVE-2026-9308?

No fix has been published for CVE-2026-9308 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-9308 being exploited?

There is no known exploitation of CVE-2026-9308 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox

- [CVE-2019-11708](https://insights.sbomify.com/CVE-2019-11708/): Mozilla Firefox and Thunderbird Sandbox Escape (critical 10.0, exploited in the wild)
- [CVE-2010-3765](https://insights.sbomify.com/CVE-2010-3765/): Mozilla Multiple Products Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26486](https://insights.sbomify.com/CVE-2022-26486/): Mozilla Firefox Use-After-Free (critical 9.6, exploited in the wild)
- [CVE-2022-26485](https://insights.sbomify.com/CVE-2022-26485/): Mozilla Firefox Use-After-Free (high 8.8, exploited in the wild)
- [CVE-2019-11707](https://insights.sbomify.com/CVE-2019-11707/): Mozilla Firefox and Thunderbird Type Confusion (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-9308 and fix it if it is affected.

What it is: CVE-2026-9308 is a medium-severity cross-site scripting vulnerability in Mozilla Firefox, published on 1 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-9308 in the wild and no public exploit code.

Affected product: Mozilla Firefox. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-9308/ (Markdown: https://insights.sbomify.com/CVE-2026-9308/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-9308
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-9308
- OSV: https://osv.dev/vulnerability/CVE-2026-9308

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-9308/
Summaries are generated and may contain mistakes; the official description above is the record.