# CVE-2026-53899: Cross-origin cookies could be leaked when opening a PDF link

> A malicious site on a suffix domain could steal cookies from a target site when a user opens a PDF link in Firefox for iOS.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:** Not needed
- **Fix available:** No
- **Published:** 16 Jun 2026
- **Updated:** 16 Jun 2026
- **Also known as:** GHSA-848m-8qg2-wmrv

## What is CVE-2026-53899?

CVE-2026-53899 is a medium-severity vulnerability in Mozilla Firefox Mobile, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Firefox for iOS used partial domain matching when attaching cookies to PDF requests, allowing a malicious site on a suffix domain to receive cookies belonging to the target site. This vulnerability was fixed in Firefox for iOS 152.0.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2026-53899?

It affects 1 product.


Products: Mozilla Firefox Mobile.

## How do I fix CVE-2026-53899?

No fix has been published for CVE-2026-53899 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-53899 being exploited?

There is no known exploitation of CVE-2026-53899 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox Mobile

- [CVE-2026-84135](https://insights.sbomify.com/CVE-2026-84135/): Other issue in Firefox Focus for Android (critical 9.8)
- [CVE-2024-43111](https://insights.sbomify.com/CVE-2024-43111/): Cross-site scripting in Firefox for iOS (critical 9.8)
- [CVE-2023-49060](https://insights.sbomify.com/CVE-2023-49060/): Information disclosure in Firefox for iOS (critical 9.8)
- [CVE-2026-92033](https://insights.sbomify.com/CVE-2026-92033/): Privilege escalation in Firefox for Android (high 8.8)
- [CVE-2026-84117](https://insights.sbomify.com/CVE-2026-84117/): Privilege escalation in Firefox for Android (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53899 and fix it if it is affected.

What it is: CVE-2026-53899 is a medium-severity vulnerability in Mozilla Firefox Mobile, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53899 in the wild and no public exploit code.

Affected product: Mozilla Firefox Mobile. 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-2026-53899/ (Markdown: https://insights.sbomify.com/CVE-2026-53899/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53899
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53899
- OSV: https://osv.dev/vulnerability/CVE-2026-53899

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53899/
Summaries are generated and may contain mistakes; the official description above is the record.