CVE-2024-6615: Mozilla Firefox RCE Vulnerability

CVE-2024-6615 Overview

CVE-2024-6615 identifies memory safety bugs in Mozilla Firefox 127 and Thunderbird 127. Mozilla developers documented multiple internal memory corruption issues during testing of these versions. Some of the bugs showed evidence of memory corruption, and Mozilla states that with sufficient effort an attacker could exploit them to run arbitrary code. The vulnerability is classified under [CWE-787] (Out-of-bounds Write) and affects Firefox versions earlier than 128 and Thunderbird versions earlier than 128. Exploitation requires a victim to load attacker-controlled content in the browser or mail client, giving the flaw a network attack vector with user interaction.

Critical Impact
Successful exploitation can lead to arbitrary code execution within the Firefox or Thunderbird process, compromising confidentiality, integrity, and availability of the affected host.

Affected Products

Mozilla Firefox versions earlier than 128
Mozilla Thunderbird versions earlier than 128
Mozilla Firefox ESR and downstream distributions shipping affected builds

Discovery Timeline

2024-07-09 - CVE-2024-6615 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-6615

Vulnerability Analysis

The issue groups multiple memory safety bugs identified internally by Mozilla in Firefox 127 and Thunderbird 127. The advisories MFSA-2024-29 and MFSA-2024-32 reference Bugzilla entries 1892875, 1894428, and 1898364. The bugs map to CWE-787, indicating out-of-bounds writes within browser memory regions. Memory corruption in a renderer or mail-parsing component can be steered into control-flow hijacking when an attacker can place crafted data adjacent to allocator metadata or function pointers.

Root Cause

The root cause is improper bounds checking in native code paths within the Gecko engine shared by Firefox and Thunderbird. Out-of-bounds writes occur when component code writes past the end of an allocated buffer. Mozilla did not publish per-bug technical detail, but the grouping is consistent with the rollup of internally found memory safety issues Mozilla publishes each release cycle.

Attack Vector

Exploitation requires the user to load attacker-controlled content. In Firefox, this typically means visiting a malicious or compromised web page. In Thunderbird, the trigger is rendering a crafted email with scripted or active content enabled. No prior authentication is required, but user interaction is needed to reach the vulnerable code path.

For technical specifics, refer to the Mozilla Bug Report List and the linked security advisories.

Detection Methods for CVE-2024-6615

Indicators of Compromise

Firefox or Thunderbird processes (firefox.exe, thunderbird.exe) crashing repeatedly with access violation or heap corruption signatures.
Unexpected child processes spawned by firefox.exe or thunderbird.exe, such as command shells, powershell.exe, or LOLBins.
Outbound network connections from the browser or mail client to uncategorized or newly registered domains immediately after rendering content.
Creation of executable files or scripts in user-writable paths shortly after a browser or mail session.

Detection Strategies

Inventory installed Firefox and Thunderbird versions across the fleet and flag any build earlier than 128.
Monitor endpoint telemetry for browser process crashes correlated with specific URLs or message identifiers.
Apply behavioral identification rules for browser-spawned shells, code-loading anomalies, and renderer sandbox escapes.

Monitoring Recommendations

Collect process lineage, module load, and network connection events from endpoints running Mozilla products.
Forward browser crash dumps and Windows Error Reporting telemetry to a central analytics pipeline.
Alert on Thunderbird child processes other than its standard helpers, especially scripting hosts or archive utilities.

How to Mitigate CVE-2024-6615

Immediate Actions Required

Upgrade Firefox to version 128 or later and Thunderbird to version 128 or later on every endpoint.
Validate package versions on managed Linux distributions and trigger forced updates through the system package manager.
Restart browser and mail client processes after the update to ensure the patched binaries are in use.

Patch Information

Mozilla addressed the issue in Firefox 128 and Thunderbird 128. See Mozilla Security Advisory MFSA-2024-29 for Firefox and Mozilla Security Advisory MFSA-2024-32 for Thunderbird. Both advisories list the same memory safety rollup and reference the underlying Bugzilla entries.

Workarounds

Disable JavaScript execution in Thunderbird for remote message content until the update is applied.
Restrict browsing to trusted destinations through web proxy policy until Firefox 128 is deployed.
Enforce strict Content Security Policy and disable risky browser features such as legacy plugins where feasible.

bash

# Configuration example: verify installed versions
firefox --version
thunderbird --version
# On Debian/Ubuntu, force update
sudo apt-get update && sudo apt-get install --only-upgrade firefox thunderbird