Firefox MobileWeb browser · Mozilla
CVE-2026-53899
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFirefox 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceFirefox for iOS used improper partial (suffix) domain matching when attaching cookies to PDF requests, allowing a malicious site on a suffix domain to receive cookies intended for the target site. This cookie leakage occurs because the browser incorrectly considers domains like attacker.legitimate.com as matching legitimate.com for cookie attachment to PDF resources.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Firefox MobileWeb browser
< 152.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Firefox for iOS installationCheck installed applications on iOS devices for Mozilla FirefoxAffected if Firefox for iOS is present on the device
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Determine Firefox for iOS versionOpen Firefox, tap the menu icon, go to Settings > Firefox Account or scroll to bottom to find version number under 'About Firefox'Affected if Version displayed is below 152.0 (e.g., 151.x, 150.x, etc.)
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Verify PDF viewing capabilityConfirm the browser can load PDF documents (default behavior when tapping PDF links or visiting sites serving PDF content)Affected if PDF viewing is enabled and used in the organization (default state)
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Assess suffix domain cookie exposureTest or audit whether PDFs are loaded from domains that could be suffix variants (e.g., attacker.legitimate.com serving PDFs meant for legitimate.com)Affected if Users load PDF documents from sites on suffix domains matching organizational domains
Organization is affected if Firefox for iOS version is below 152.0 on managed devices and users potentially load PDF content from suffix-match domains.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped152.0
Update Firefox for iOS to version 152.0 or later on all affected devices. Organizations should use MDM or equivalent tooling to verify browser versions and ensure the update is deployed.
Firefox for iOS 152.0
- Open the App Store on your iOS device
- Search for "Firefox" in the App Store
- Tap the Update button next to Firefox to update to version 152.0
- Alternatively, go to the Firefox product page in the App Store and tap Update if an update is available
- Ensure the update completes successfully before using the browser
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox Mobile
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-53899 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-53899 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data