CVE-2024-1557: Mozilla Firefox RCE Vulnerability

CVE-2024-1557 Overview

CVE-2024-1557 describes memory safety bugs present in Mozilla Firefox 122. Mozilla developers identified internal memory corruption issues across multiple components of the browser engine. Some of these bugs showed evidence of memory corruption that, with sufficient effort, could be exploited to run arbitrary code in the context of the browser process.

The vulnerability affects all Firefox versions prior to 123. It is classified under [CWE-787] Out-of-bounds Write and carries a network-based attack vector with no privileges or user interaction required beyond standard browsing activity.

Critical Impact

Successful exploitation could lead to arbitrary code execution within the Firefox process, compromising confidentiality, integrity, and availability of the browser and any data it handles.

Affected Products

• Mozilla Firefox versions prior to 123
• Mozilla Firefox 122 (primary affected release)
• Builds tracked under Mozilla Foundation Security Advisory MFSA-2024-05

Discovery Timeline

• 2024-02-20 - CVE-2024-1557 published to NVD
• 2025-05-06 - Last updated in NVD database

Technical Details for CVE-2024-1557

Vulnerability Analysis

CVE-2024-1557 aggregates multiple memory safety defects identified by Mozilla developers during Firefox 122 testing. The defects span several browser subsystems and include conditions consistent with out-of-bounds writes [CWE-787]. Mozilla reported that some of these bugs showed evidence of memory corruption during fuzzing and triage.

Memory corruption flaws in browser engines typically arise in code paths handling untrusted content such as HTML parsing, JavaScript engine internals, graphics rendering, or media decoding. When attacker-controlled data overwrites adjacent memory, an attacker can manipulate object metadata, function pointers, or virtual table entries to redirect execution.

The public bug list referenced by Mozilla (bugs 1746471, 1848829, 1864011, 1869175, 1869455, 1869938, 1871606) consolidates the individual reports rolled up into this single CVE entry. Exploitation requires that a user load attacker-controlled web content in an unpatched Firefox 122 build.

Root Cause

The root cause is improper bounds enforcement in multiple Firefox 122 components, mapped to [CWE-787] Out-of-bounds Write. When parsing or processing untrusted input, affected code paths write past allocated buffer boundaries, corrupting adjacent heap or stack memory.

Attack Vector

An attacker hosts a malicious page or compromises a legitimate site to deliver crafted content. The victim visits the page using an unpatched Firefox 122 build, which triggers the memory corruption during content processing. No authentication is required, and exploitation succeeds without additional user interaction beyond page navigation.

The vulnerability is described in prose by Mozilla rather than with public proof-of-concept code. No public exploit is currently available, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog. See the Mozilla Security Advisory MFSA-2024-05 for vendor details.

Detection Methods for CVE-2024-1557

Indicators of Compromise

• Firefox processes crashing with access violations, segmentation faults, or EXCEPTION_ACCESS_VIOLATION events while browsing untrusted content.
• Unexpected child processes spawned from firefox.exe or the Firefox content process, such as command shells or scripting hosts.
• Outbound network connections from Firefox child processes to unfamiliar infrastructure shortly after page loads.

Detection Strategies

• Inventory installed Firefox versions across managed endpoints and flag any build earlier than 123.
• Monitor crash telemetry and Windows Error Reporting data for repeated Firefox content process crashes correlated with specific URLs.
• Correlate browser process activity with EDR telemetry to identify post-exploitation behavior such as process injection or credential access.

Monitoring Recommendations

• Aggregate browser version inventory into a central log source and alert when out-of-date Firefox installs are observed.
• Watch for anomalous file writes by firefox.exe to autostart locations, scheduled task paths, or user profile script directories.
• Track DNS and HTTP telemetry for domains delivering known malicious or fingerprinting content to Firefox clients.

How to Mitigate CVE-2024-1557

Immediate Actions Required

• Update Firefox to version 123 or later on all managed and unmanaged endpoints.
• Restart browser sessions after upgrade to ensure the patched binary is loaded into memory.
• Identify legacy or pinned Firefox 122 deployments in development, testing, or kiosk environments and prioritize their remediation.

Patch Information

Mozilla addressed the memory safety bugs in Firefox 123. The fix is documented in Mozilla Security Advisory MFSA-2024-05, with underlying bug references published in the Mozilla Bug List. Administrators using enterprise deployment channels should validate that update policies are not blocking Firefox 123 or later builds.

Workarounds

• Restrict browsing on unpatched hosts to trusted internal sites until Firefox can be updated.
• Apply web proxy or DNS filtering to block known malicious domains and limit exposure to untrusted content.
• Enforce least-privilege user accounts so that any successful exploitation runs without administrative rights.

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

# Windows: query installed version via registry
reg query "HKLM\SOFTWARE\Mozilla\Mozilla Firefox" /v CurrentVersion

# macOS: read bundle version
defaults read /Applications/Firefox.app/Contents/Info CFBundleShortVersionString