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.

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

Q: 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.

Q: How is CVE-2026-53900 attacked?

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

Q: 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.

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. 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

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