Is CVE-2026-53899 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-53899 being exploited in the wild.

How severe is CVE-2026-53899?

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-2026-53899?

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-2026-53899 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-53899?

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.

CVE-2026-53899: Mozilla Firefox for iOS cookie leakage in PDF requests

Q: Is there a fix for CVE-2026-53899?

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.

Q: How is CVE-2026-53899 attacked?

It is attacked over the network, in a network appliance.

Q: Am I affected by CVE-2026-53899?

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.

CVE-2026-53899 · Severity: info · CVSS 7.5 · Published 2026-06-16

A security flaw in Firefox for iOS could allow malicious websites to steal sensitive login cookies from other sites. This occurs when the browser incorrectly shares authentication data while opening PDF documents. An attacker could use this to gain unauthorized access to a user's web accounts if the user visits a specially crafted link.

Technologies: Mozilla Firefox for iOS. Vendors: Mozilla.

Quick answers

Is CVE-2026-53899 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-53899 being exploited in the wild.
How severe is CVE-2026-53899?: 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-2026-53899?: 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-2026-53899 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-53899?: 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 vulnerability in Firefox for iOS stems from an improper implementation of domain matching logic within the PDF request handler. Specifically, the browser used partial domain matching (suffix matching) when determining which cookies to attach to a request for a PDF document. This allows a malicious site hosted on a suffix domain to receive cookies intended for a different target domain. An attacker can exploit this by enticing a user to click a link to a PDF, potentially resulting in the disclosure of sensitive session tokens or authentication cookies. The issue is resolved in Firefox for iOS version 152.0.

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

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