# CVE-2026-53900: Mozilla Firefox for iOS cookie injection via PDF redirect

Source: https://junglewise.ai/threats/cve-2026-53900-mozilla-firefox-for-ios-cookie-injection-via-pdf-redirect  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-16. Updated: 2026-06-16  
License: CC BY 4.0 with a link back

CVE-2026-53900 · Severity: info · CVSS 7.5 · Published 2026-06-16

Mozilla Firefox for iOS contained a flaw in how it handled PDF downloads that could allow a malicious website to interfere with a user's session on other websites. By using a specially crafted redirect, an attacker could force the browser to send unauthorized cookies to a different, unrelated domain. This could potentially lead to session fixation or other attacks where the attacker controls the state of a user's account on a target service.

Technologies: [Mozilla Firefox for iOS](https://junglewise.ai/threats/technologies/firefox-for-ios). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2026-53900 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-53900 being exploited in the wild.

**How severe is CVE-2026-53900?** Informational severity, with a CVSS score of 7.5, published 16 June 2026.

**Which products and versions are affected?** Mozilla Firefox for iOS < 152.0.

**Is there a fix for CVE-2026-53900?** A patch was published on 2026-06-16: Fixed in Firefox for iOS 152.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-53900 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-53900?** Check whether you run Mozilla Firefox for iOS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A cookie injection vulnerability existed in Firefox for iOS within the TemporaryDocument component. When a user initiated a request for a PDF, the browser preserved cookies set during the initial request even if the request was subsequently redirected to a different origin (cross-origin HTTP redirect). An attacker could leverage this behavior to inject arbitrary cookies into requests destined for an unrelated target domain. This bypasses the Same-Origin Policy (SOP) protections for cookie handling during redirects. The issue was addressed in Firefox for iOS version 152.0 by ensuring cookies are not improperly preserved across cross-origin redirects for these document types.

## Affected products

- Mozilla Firefox for iOS < 152.0

## Timeline

- 2026-06-16: disclosed
- 2026-06-16: advisory
- 2026-06-16: patched: Fixed in Firefox for iOS 152.0

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2043204](https://bugzilla.mozilla.org/show_bug.cgi?id=2043204)
- [https://www.mozilla.org/security/advisories/mfsa2026-56/](https://www.mozilla.org/security/advisories/mfsa2026-56/)

## Related threats

- [Mozilla Firefox for iOS privilege escalation](https://junglewise.ai/threats/cve-2026-121843-privilege-escalation-in-firefox-for-ios-this-vulnerability-was)
- [Mozilla Firefox for iOS privilege escalation in Reader View](https://junglewise.ai/threats/cve-2026-121842-privilege-escalation-in-the-reader-view-component-in-firefox-for)
- [Firefox for iOS information disclosure](https://junglewise.ai/threats/cve-2026-121841-other-issue-in-firefox-for-ios-this-vulnerability-was-fixed-in)
- [Firefox for iOS FaceTime protocol handler spoofing](https://junglewise.ai/threats/cve-2026-116632-a-malicious-web-page-could-insert-arbitrary-text-into-the)
- [Firefox for iOS external protocol handler spoofing via tel link](https://junglewise.ai/threats/cve-2026-116631-a-malicious-web-page-could-open-a-tel-link-in-a-window-that-was)