Memory disclosure via incorrect canvas export stride
Published Apr 21, 2026 · Updated Jul 15, 2026
Canvas2D disclosure in Mozilla Firefox on Red Hat Enterprise Linux allows remote attackers to read heap bytes via crafted web content. ImageEncoder::ExtractDataInternal passes width times four as the row stride when exporting a transferred canvas with toDataURL(), causing aligned surface padding containing uninitialized memory to become image pixels. Exploitation requires scripted canvas rendering, including the demonstrated alpha-enabled WebGL path; the demonstrated consequence is memory disclosure, and Thunderbird disables scripting in normal mail views.
Summary
What happened
Canvas2D disclosure in Mozilla Firefox on Red Hat Enterprise Linux allows remote attackers to read heap bytes via crafted web content. ImageEncoder::ExtractDataInternal passes width times four as the row stride when exporting a transferred canvas with toDataURL(), causing aligned surface padding containing uninitialized memory to become image pixels. Exploitation requires scripted canvas rendering, including the demonstrated alpha-enabled WebGL path; the demonstrated consequence is memory disclosure, and Thunderbird disables scripting in normal mail views.
The record
- CVE
- CVE-2026-6749
- Published
- Apr 21, 2026
- Updated
- Jul 15, 2026
- Vendor
- libuser Project
- Product
- Red Hat Enterprise Linux 9
- Classifications
- CWE-908, CWE-824
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 21, 2026CVE publishedPublication date reported by the CVE source.
- Jul 15, 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?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
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.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
- poc_transferred_offscreencanvas_padding.htmlproof of concept · demonstrated
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Technologies
Your stack
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