CVE-2026-53900: Firefox for iOS preserved cookies set on the initial PDF request across cross-origin HTTP redirects in Tempora

Q: How do I fix CVE-2026-53900?

firefox mobile: upgrade to 152.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-53900 being exploited?

CVE-2026-53900 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-53900 affect?

CVE-2026-53900 affects firefox mobile. Severity is medium (CVSS 4.3). Firefox for iOS preserved cookies set on the initial PDF request across cross-origin HTTP redirects in TemporaryDocument, allowing a malicious site to inject arbitrary cookies into requests to an unrelated target domain. This vulnerability

Q: How urgent is CVE-2026-53900?

Priority 15/100. No elevated risk signals yet.

Routine

MEDIUM 4.3UPGRADE

CVE-2026-53900 is a medium-severity flaw (CVSS 4.3) affecting firefox mobile. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Firefox for iOS preserved cookies set on the initial PDF request across cross-origin HTTP redirects in TemporaryDocument, allowing a malicious site to inject arbitrary cookies into requests to an unrelated target domain. This vulnerability was fixed in Firefox for iOS 152.0.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.1% (top 99%)
CISA exploited list	No
Weakness	CWE-345, CWE-384
Published	2026-06-16
Last modified	2026-10-26

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-16 13:16 UTCPublished CVE record published
2026-10-26 12:10 UTCUpdated Record last modified

mozilla firefox mobile UPGRADE

Affected: < 152.0

Fixed in: 152.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy firefox-mobile || rpm -q firefox-mobile || firefox-mobile --version

2. UPGRADE to 152.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade firefox-mobile

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firefox-mobile

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-53900?

firefox mobile: upgrade to 152.0. Exact commands for each OS are on this page.

Is CVE-2026-53900 being exploited?

CVE-2026-53900 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-53900 affect?

CVE-2026-53900 affects firefox mobile. Severity is medium (CVSS 4.3). Firefox for iOS preserved cookies set on the initial PDF request across cross-origin HTTP redirects in TemporaryDocument, allowing a malicious site to inject arbitrary cookies into requests to an unrelated target domain. This vulnerability

How urgent is CVE-2026-53900?

Priority 15/100. No elevated risk signals yet.

Software pages

iOS vulnerabilities · Mozilla Firefox vulnerabilities

Related CVEs

CVE-2026-53899 MEDIUM 6.5 UPGRADE Firefox for iOS used partial domain matching when attaching cookies to PDF requests, allowing a malicious site
CVE-2026-14906 MEDIUM 5.3 UPGRADE Pages with malicious titles could potentially allow saved PDF content to overwrite PDF files or bundled conten
CVE-2026-16373 HIGH 7.5 UPGRADE Information disclosure in the Privacy component in Firefox for Android
CVE-2026-16404 HIGH 7.4 UPGRADE Spoofing issue in Firefox for Android
CVE-2023-29550 HIGH 8.8 UPGRADE UPGRADE Memory safety bugs present in Firefox 111 and Firefox ESR 102.9

References

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