CVE-2016-9900

CVE-2016-9900 is a high-severity vulnerability in Mozilla Thunderbird with a CVSS 3.x base score of 7.5. 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-254.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v2: 5.0
• EPSS exploit prediction: 10% (95th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-254
• Affected product: Mozilla Thunderbird
• Published: 2018-06-11
• Last modified: 2026-06-17

Description

External resources that should be blocked when loaded by SVG images can bypass security restrictions through the use of "data:" URLs. This could allow for cross-domain data leakage. This vulnerability affects Firefox < 50.1, Firefox ESR < 45.6, and Thunderbird < 45.6.

Frequently asked questions

What is CVE-2016-9900?

External resources that should be blocked when loaded by SVG images can bypass security restrictions through the use of "data:" URLs. This could allow for cross-domain data leakage. This vulnerability affects Firefox < 50.1, Firefox ESR < 45.6, and Thunderbird < 45.6.

How severe is CVE-2016-9900?

CVE-2016-9900 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2016-9900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 10% (95th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-9900?

CVE-2016-9900 primarily affects Mozilla Thunderbird. In total, 20 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-9900?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2016-9900 published?

CVE-2016-9900 was published on 2018-06-11 and last updated on 2026-06-17.

References

• http://rhn.redhat.com/errata/RHSA-2016-2946.html
• http://rhn.redhat.com/errata/RHSA-2016-2973.html
• http://www.securityfocus.com/bid/94885
• http://www.securitytracker.com/id/1037461
• https://bugzilla.mozilla.org/show_bug.cgi?id=1319122
• https://security.gentoo.org/glsa/201701-15
• https://www.debian.org/security/2017/dsa-3757
• https://www.mozilla.org/security/advisories/mfsa2016-94/
• https://www.mozilla.org/security/advisories/mfsa2016-95/
• https://www.mozilla.org/security/advisories/mfsa2016-96/

Affected products (20)

• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:5.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_desktop:5.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_desktop:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_desktop:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server:5.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:7.3:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:7.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_eus:7.3:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_eus:7.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_eus:7.5:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_workstation:5.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_workstation:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_workstation:7.0:*:*:*:*:*:*:*
• cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
• cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

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