CVE-2026-6783: 
NixOS vulnerability analysis and mitigation

CVE-2026-6783 is an incorrect boundary conditions and integer overflow vulnerability in the Audio/Video: Playback component of Mozilla Firefox and Thunderbird. Discovered by researcher "crixer" and disclosed on April 21, 2026, it affects Firefox and Thunderbird versions prior to 150.0. The vulnerability was fixed in Firefox 150 and Thunderbird 150. It carries a CVSS v3.1 base score of 5.3 (Medium) (Mozilla Advisory, GitHub Advisory).

The vulnerability is classified as CWE-190 (Integer Overflow or Wraparound), arising from incorrect boundary conditions in the Audio/Video: Playback component of Firefox and Thunderbird. An integer overflow occurs when a calculated value exceeds the maximum representable size for its data type, potentially causing the value to wrap around to a very small or negative number, leading to unexpected behavior such as out-of-bounds memory access or logic errors. The flaw is exploitable remotely over the network without authentication or user interaction, as reflected in the CVSS attack vector. The underlying bug is tracked in Mozilla's Bugzilla as Bug 2027564, though the bug report requires permissions to access (Mozilla Advisory, GitHub Advisory).

Successful exploitation of CVE-2026-6783 results in a low-integrity impact with no confidentiality or availability consequences, as reflected in the CVSS scoring. An attacker could potentially manipulate data processed by the Audio/Video: Playback component due to the integer overflow, leading to unintended behavior or minor data integrity violations. Mozilla rated the overall impact of this vulnerability as "low" within the Firefox 150 advisory, indicating limited practical risk compared to higher-severity issues patched in the same release (Mozilla Advisory).

There is no known public proof-of-concept exploit or evidence of in-the-wild exploitation for CVE-2026-6783 at this time. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.027%–0.041%, placing it in the 13th percentile for exploitation likelihood within 30 days, indicating a low probability of active exploitation (GitHub Advisory). No threat actor attribution has been reported.

Mozilla has released patches addressing this vulnerability in Firefox 150 and Thunderbird 150, both announced on April 21, 2026. Users and administrators should update Firefox and Thunderbird to version 150.0 or later immediately. No configuration-based workarounds have been published; upgrading to the patched version is the only recommended remediation (Mozilla Advisory mfsa2026-30, Mozilla Advisory mfsa2026-33).

The CIS (Center for Internet Security) published an advisory noting that multiple vulnerabilities in Mozilla products fixed in Firefox 150 could allow for arbitrary code execution, grouping CVE-2026-6783 among the broader set of issues addressed in the release. Security media outlets including GBHackers and CyberPress covered the Firefox 150 release, highlighting the range of vulnerabilities patched. No specific notable researcher commentary or significant social media discussion focused exclusively on CVE-2026-6783 has been identified, consistent with its low-severity rating.