Rule Category

BROWSER-FIREFOX -- Snort has detected traffic known to exploit vulnerabilities present in the Firefox browser, or products that have the "Gecko" engine (Thunderbird email client, etc.).

Alert Message

BROWSER-FIREFOX Mozilla Firefox ReadableStreamCloseInternal out-of-bounds access attempt

Rule Explanation

This rule looks for a certain sequence of JavaScript operations that are designed to cause a state inconsistency bug to manifest, leading to an out-of-bounds read. This bug could be exploited to corrupt memory, potentially leading to arbitrary remote code execution.

What To Look For

This rule alerts when a specifically formatted web page designed to exploit CVE-2020-6806 is detected. CVE-2020-6806 is a memory corruption bug in Mozilla Firefox.

Known Usage

No public information

False Positives

No known false positives


Cisco Talos Intelligence Group

Rule Groups

No rule groups


Additional Links

Rule Vulnerability

CVE Additional Information

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.
Severity Base Score8.8
Impact Score5.9 Exploit Score2.8
Confidentiality ImpactHIGH Integrity ImpactHIGH
Availability ImpactHIGH Attack VectorNETWORK
Authentication Ease of AccessLOW
Privileges RequiredNONE