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CVE-2026-74943 is a use-after-free vulnerability in Mozilla's Graphics: ImageLib component affecting Firefox, Firefox ESR, and Thunderbird. The flaw arises from incorrect lifetime management of memory in ImageLib, allowing previously freed memory to be reused. This can result in memory corruption during processing of attacker-influenced content in the affected application. Mozilla reports the issue as fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a small standalone proof-of-concept for CVE-2026-74943, a use-after-free in Mozilla Firefox's RasterImage / SurfaceCache interaction. The repo contains three files: a README describing the root cause and affected versions, prefs.js with recommended Firefox settings to make reproduction more reliable, and uaf-reduced.html containing the actual browser testcase. The exploit capability is limited to vulnerability reproduction: it repeatedly creates a blob-backed child HTML page inside an iframe, generates many unique canvas-rendered PNG images, waits for decode completion, and then removes the iframe so the associated RasterImage objects are torn down while the decoder thread is evicting surfaces from a deliberately tiny cache. This creates pressure on the vulnerable OnSurfaceDiscarded path and can trigger an intermittent heap use-after-free in the content process. No post-exploitation payload, shell, persistence, or command execution is included. The structure is straightforward: README.md documents the race condition, impact, and fix; prefs.js tunes Firefox runtime behavior for testing; uaf-reduced.html is the main entry point and contains all trigger logic in inline JavaScript. The testcase uses only local browser primitives (Blob URLs, iframe creation/removal, canvas drawing, Image.decode, and data URLs) and does not contact external network infrastructure. Overall, this is a legitimate browser-based POC exploit for reproducing a memory safety bug, best classified as a proof-of-concept rather than an operational or weaponized exploit.
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13 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A specific vulnerability affecting Debian 13 firefox-esr packages; no further technical details are provided in the content.
A specific published vulnerability tracked as CVE-2026-74943 affecting Linux distributions and related Mozilla package builds such as Firefox, Thunderbird, and mozjs packages, as indicated by the listed CPEs and package CPEs.
Unknown; listed as one of multiple vulnerabilities addressed by Mozilla Thunderbird 140.14.
A vulnerability affecting Mozilla Thunderbird, referenced by a Tenable plugin for macOS Thunderbird 140.14.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.