Memory disclosure via unchecked AVIF offset
Published Feb 24, 2026 · Updated Feb 24, 2026
An out-of-bounds read in Mozilla Firefox, Firefox ESR, and Thunderbird allows remote attackers to read process memory via crafted AVIF content. AVIFDecoderStream::ReadAt subtracts an unvalidated signed offset from the buffer length, converts the result to an unsigned size, and passes the oversized range to memcpy. Processing attacker-controlled AVIF content reaches the flaw; the demonstrated consequence is a read beyond the image buffer, not code execution.
Summary
What happened
An out-of-bounds read in Mozilla Firefox, Firefox ESR, and Thunderbird allows remote attackers to read process memory via crafted AVIF content. AVIFDecoderStream::ReadAt subtracts an unvalidated signed offset from the buffer length, converts the result to an unsigned size, and passes the oversized range to memcpy. Processing attacker-controlled AVIF content reaches the flaw; the demonstrated consequence is a read beyond the image buffer, not code execution.
The record
- CVE
- CVE-2026-2759
- Published
- Feb 24, 2026
- Updated
- Feb 24, 2026
- Vendor
- Mozilla
- Product
- Firefox
- Classifications
- CWE-1384, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 24, 2026CVE publishedPublication date reported by the CVE source.
- Feb 24, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=unspecified <148
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Minimal AVIFDecoderStream out-of-bounds read proof of conceptproof of concept · unverified
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Technologies
Your stack
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Your stack
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