How severe is CVE-2026-53900?

CVE-2026-53900 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-53900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-53900?

CVE-2026-53900 affects Mozilla Firefox Mobile. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-53900?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-53900 have an EU (EUVD) identifier?

Yes. CVE-2026-53900 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37078.

When was CVE-2026-53900 published?

CVE-2026-53900 was published on 2026-06-16 and last updated on 2026-06-17.

CVE-2026-53900

CVE-2026-53900 is a medium-severity vulnerability in Mozilla Firefox Mobile with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
EPSS exploit prediction: 0% (1st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37078
Weakness: CWE-345
Affected product: Mozilla Firefox Mobile
Published: 2026-06-16
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-53900?: 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.
How severe is CVE-2026-53900?: CVE-2026-53900 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-53900 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-53900?: CVE-2026-53900 affects Mozilla Firefox Mobile. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-53900?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-53900 have an EU (EUVD) identifier?: Yes. CVE-2026-53900 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37078.
When was CVE-2026-53900 published?: CVE-2026-53900 was published on 2026-06-16 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mozilla:firefox_mobile:*:*:*:*:*:iphone_os:*:*

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