CVE-2024-6606: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2024-6606 Overview

CVE-2024-6606 is an out-of-bounds read vulnerability in Mozilla Firefox and Thunderbird clipboard handling code. The clipboard code failed to validate an array index before access, allowing reads beyond the intended buffer boundary. The flaw affects Firefox versions before 128 and Thunderbird versions before 128. Mozilla addressed the issue in security advisories MFSA-2024-29 and MFSA-2024-32. The vulnerability is categorized under [CWE-125] (Out-of-bounds Read) and requires user interaction to trigger, typically through clipboard operations initiated on a malicious page.

Critical Impact

Successful exploitation can disclose sensitive process memory from the browser, potentially exposing credentials, tokens, or other data adjacent to the clipboard buffer.

Affected Products

• Mozilla Firefox versions prior to 128
• Mozilla Thunderbird versions prior to 128
• Platforms: Windows, macOS, and Linux builds of the affected browsers

Discovery Timeline

• 2024-07-09 - CVE-2024-6606 published to NVD
• 2025-04-04 - Last updated in NVD database

Technical Details for CVE-2024-6606

Vulnerability Analysis

The vulnerability stems from missing bounds validation in Firefox and Thunderbird clipboard handling logic. Clipboard code accessed an array element without verifying that the supplied index fell within the allocated range. When an out-of-range index is used, the read operation returns adjacent memory contents that lie outside the intended buffer.

Out-of-bounds reads in browser process memory can expose pointer values, heap metadata, or residual user data. Attackers can chain such leaks with other vulnerabilities to defeat Address Space Layout Randomization (ASLR) or to extract sensitive content from the renderer process. The scope-changed nature of this issue indicates the read can cross trust boundaries inside the browser.

Root Cause

The root cause is improper input validation on an array index used during clipboard processing. The code path performed the access without confirming the index was less than the array length, producing a classic [CWE-125] condition. Mozilla's fix introduces the missing bounds check before the access occurs, as referenced in Mozilla Bug Report #1902305.

Attack Vector

Exploitation requires user interaction, such as visiting a crafted web page in Firefox or rendering hostile HTML content in Thunderbird. The attacker triggers a clipboard operation that supplies attacker-controlled state, causing the unchecked index to be used. The network attack vector and lack of required privileges make drive-by exploitation feasible against unpatched clients. No public proof-of-concept exploit or in-the-wild exploitation has been reported, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2024-6606

Indicators of Compromise

• Firefox or Thunderbird processes with versions below 128 still present in software inventory after July 2024
• Browser process crashes or unexpected memory pressure during clipboard interactions
• Outbound connections from browser processes to attacker-controlled URLs immediately following clipboard events

Detection Strategies

• Inventory endpoints for installed Firefox and Thunderbird builds and compare against version 128 or later
• Hunt for renderer process exceptions correlated with clipboard paste or copy events in browser telemetry
• Review web proxy logs for pages invoking unusual clipboard APIs followed by data exfiltration patterns

Monitoring Recommendations

• Forward browser application logs and endpoint process telemetry to a central analytics platform for correlation
• Alert on Firefox or Thunderbird child process crashes that reference clipboard or content modules
• Track patch deployment status for Mozilla products as a recurring vulnerability management metric

How to Mitigate CVE-2024-6606

Immediate Actions Required

• Upgrade Mozilla Firefox to version 128 or later on all managed endpoints
• Upgrade Mozilla Thunderbird to version 128 or later, including ESR channels where applicable
• Validate the patched version is enforced through software distribution tooling and block downgrades

Patch Information

Mozilla released fixes in Firefox 128 and Thunderbird 128. Refer to the Mozilla Security Advisory MFSA-2024-29 for Firefox and the Mozilla Security Advisory MFSA-2024-32 for Thunderbird. The underlying code change is tracked in Mozilla Bug Report #1902305.

Workarounds

• Restrict use of Firefox and Thunderbird below version 128 through application control policies until patching completes
• Disable rendering of remote content in Thunderbird to reduce exposure from email-borne triggers
• Apply enterprise policies that prevent untrusted sites from invoking the Clipboard API where supported

# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify installed Thunderbird version
thunderbird --version

# Example: enforce minimum version via policy file (Linux)
cat /etc/firefox/policies/policies.json