CVE-2026-6785

Description

Memory safety bugs present in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

CVSS Details

CVSS Score

8.1

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

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

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

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

Firefox < 150

Firefox ESR < 115.35

Firefox ESR < 140.10

Thunderbird < 150

Thunderbird ESR < 140.10

PoC / Exploit Code

⚠ For Security Research Only

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

python

<!-- 
   Conceptual PoC for Memory Corruption vulnerability 
   This script attempts to trigger a crash via heap spraying pattern.
-->
<html>
<body>
<script>
   // Simulate heap corruption
   var buffer = new ArrayBuffer(0x100000);
   var view = new Uint8Array(buffer);
   for (var i = 0; i < view.length; i++) {
       view[i] = 0x41; // 'A'
   }
   // Trigger potential vulnerability point
   function trigger() {
       // Placeholder for specific vulnerable function call
       location.reload();
   }
   setTimeout(trigger, 1000);
</script>
</body>
</html>

References

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-6785", "sourceIdentifier": "[email protected]", "published": "2026-04-26T19:53:39.010", "lastModified": "2026-04-28T19:45:35.750", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Memory safety bugs present in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, 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:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 5.9}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-125"}, {"lang": "en", "value": "CWE-416"}, {"lang": "en", "value": "CWE-787"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*", "versionEndExcluding": "115.35.0", "matchCriteriaId": "E69D71F5-CAAA-4F28-AB9F-9F898A52D506"}, {"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:firefox:*:*:*:*:esr:*:*:*", "versionStartIncluding": "140.0", "versionEndExcluding": "140.10.0", "matchCriteriaId": "528443E0-C15A-4E70-9187-8E1BAAE84A42"}, {"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/buglist.cgi?bug_id=1935995%2C1999158%2C2015952%2C2021909%2C2022026%2C2022041%2C2022088%2C2022276%2C2022335%2C2022338%2C2022373%2C2022597%2C2022874%2C2023276%2C2023544%2C2023551%2C2023599%2C2023608%2C2023814%2C2024233%2C2024239%2C2024241%2C2024242%2C2024250%2C2024251%2C2024343%2C2024422%2C2024425%2C2024440%2C2024442%2C2024446%2C2024458%2C2024463%2C2024478%2C2024650%2C2024653%2C2024654%2C2024655%2C2024656%2C2024661%2C2024662%2C2024668%2C2024919%2C2025278%2C2025349%2C2025350%2C2025354%2C2025360%2C2025363%2C2025370%2C2025379%2C2025381%2C2025399%2C2025400%2C2025403%2C2025407%2C2025415%2C2025420%2C2025427%2C2025429%2C2025430%2C2025479%2C2025489%2C2025493%2C2025497%2C2025502%2C2025515%2C2025517%2C2025526%2C2025609%2C2025948%2C2025949%2C2025951%2C2025953%2C2025955%2C2025962%2C2025969%2C2025970%2C2025971%2C2025973%2C2025976%2C2025977%2C2026280%2C2026285%2C2026293%2C2026296%2C2026310%2C2027237%2C2027260%2C2027268%2C2027277%2C2027284%2C2027291%2C2027293%2C2027298%2C2027330%2C2027342%2C2027345%2C2027359%2C2027365%2C2027378%2C2027754%2C2027959%2C2027962%2C2027964%2C2027971%2C2027974%2C2027979%2C2027982%2C2027995%2C2028001%2C2028267%2C2028268%2C2028275%2C2028288%2C2028290%2C2028291%2C2028528%2C2028551%2C2028627%2C2028879%2C2028889%2C2029061%2C2029071%2C2029283%2C2029296%2C2029314%2C2029323%2C2029411%2C2029423%2C2029424%2C2029425%2C2029427%2C2029436%2C2029440%2C2029449%2C2029450%2C2029458%2C2029462%2C2029468%2C2029472%2C2029690%2C2029707%2C2029708%2C2029728%2C2029802%2C2029896%2C2029906%2C2030106%2C2030118%2C2030123%2C2030135%2C2030230%2C2030320", "source": "[email protected]", "tags": ["Broken Link"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-30/", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.mozilla.org/security/advisories/mfsa2026-31/", "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"]}]}}