What’s Vulnerable › Vulnerabilities

CVE-2020-6806

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-03-25 · updated 2026-06-17
• Weakness: CWE-125

Description

By carefully crafting promise resolutions, it was possible to cause an out-of-bounds read off the end of an array resized during script execution. This could have led to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 68.6, Firefox < 74, Firefox < ESR68.6, and Firefox ESR < 68.6.

Affected products

• Canonical Ubuntu Linux: 16.04, 18.04, 19.10
• Mozilla Firefox: before 74.0 — fixed in 74.0
• Mozilla Firefox ESR: before 68.6.0 — fixed in 68.6.0
• Mozilla Thunderbird: before 68.6.0 — fixed in 68.6.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 74.0; Mozilla Firefox ESR 68.6.0; Mozilla Thunderbird 68.6.0. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/157524/Firefox-js-ReadableStreamCloseInternal-Out-Of-Bounds-Access.html
• https://bugzilla.mozilla.org/show_bug.cgi?id=1612308
• https://usn.ubuntu.com/4328-1/
• https://usn.ubuntu.com/4335-1/
• https://www.mozilla.org/security/advisories/mfsa2020-08/
• https://www.mozilla.org/security/advisories/mfsa2020-09/
• https://www.mozilla.org/security/advisories/mfsa2020-10/
• http://packetstormsecurity.com/files/157524/Firefox-js-ReadableStreamCloseInternal-Out-Of-Bounds-Access.html
• https://bugzilla.mozilla.org/show_bug.cgi?id=1612308
• https://usn.ubuntu.com/4328-1/
• https://usn.ubuntu.com/4335-1/
• https://www.mozilla.org/security/advisories/mfsa2020-08/

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