CVE-2025-4092 Overview
CVE-2025-4092 tracks a set of memory safety bugs affecting Mozilla Firefox 137 and Mozilla Thunderbird 137. Mozilla developers identified evidence of memory corruption in several of the reported issues. With sufficient effort, attackers could potentially leverage some of these bugs to run arbitrary code within the affected process.
Mozilla addressed the flaws in Firefox 138 and Thunderbird 138. The weakness class is categorized under [CWE-119], improper restriction of operations within the bounds of a memory buffer.
Critical Impact
Successful exploitation could lead to arbitrary code execution in the context of the browser or mail client process, exposing user data and enabling further attacker actions.
Affected Products
- Mozilla Firefox versions prior to 138
- Mozilla Thunderbird versions prior to 138
- All platforms where the affected Mozilla clients are deployed
Discovery Timeline
- 2025-04-29 - CVE-2025-4092 published to the National Vulnerability Database
- 2026-06-17 - Last updated in the NVD database
Technical Details for CVE-2025-4092
Vulnerability Analysis
CVE-2025-4092 aggregates multiple memory safety defects reported through Mozilla's internal fuzzing and testing programs. Mozilla stated that some of the underlying bugs showed evidence of memory corruption. Memory corruption in browser engines commonly arises from use-after-free conditions, out-of-bounds reads or writes, and type confusion inside JavaScript engine, layout, or graphics components.
The attack vector is network-based and requires no authentication or user interaction beyond loading web content. An attacker capable of serving malicious HTML, CSS, JavaScript, or crafted email content to a vulnerable Firefox or Thunderbird instance can trigger the flawed code paths. Impact focuses on confidentiality and integrity within the affected renderer process.
Root Cause
The root cause is improper restriction of operations within the bounds of a memory buffer [CWE-119] across shared Gecko platform code used by both Firefox 137 and Thunderbird 137. Specific bug reports are tracked in Mozilla Bugzilla entries 1924108, 1950780, and 1959367, which contain the code-level fixes shipped in the 138 release train.
Attack Vector
Exploitation follows the standard browser exploitation pattern. An attacker hosts a crafted web page or delivers malicious HTML content through email in Thunderbird. When the victim's client renders the content, the memory corruption is triggered inside the parsing or rendering pipeline. A weaponized payload could shape the heap, control freed object contents, and pivot to arbitrary code execution inside the sandboxed content process.
No public proof-of-concept exploit is available. CISA has not listed CVE-2025-4092 in the Known Exploited Vulnerabilities catalog. Refer to Mozilla Security Advisory MFSA-2025-28 and Mozilla Security Advisory MFSA-2025-31 for vendor-provided technical detail.
Detection Methods for CVE-2025-4092
Indicators of Compromise
- Unexpected crashes or SIGSEGV events originating from firefox.exe, thunderbird.exe, or the corresponding content processes on Linux and macOS
- New or unusual child processes spawned by Firefox or Thunderbird outside the standard sandboxed content process tree
- Outbound network connections from browser child processes to previously unseen infrastructure shortly after loading untrusted content
Detection Strategies
- Inventory endpoint software to identify hosts still running Firefox or Thunderbird 137 or earlier and flag them for remediation
- Alert on browser or mail client processes crashing repeatedly on the same host, which may indicate exploitation attempts against memory safety bugs
- Correlate browser process anomalies with recent inbound email or web navigation events to attribute suspicious activity
Monitoring Recommendations
- Ingest endpoint process, file, and network telemetry into a centralized analytics platform to identify browser-based exploitation patterns
- Monitor Mozilla's advisory feed for follow-on fixes referencing bug IDs 1924108, 1950780, and 1959367
- Track user-agent strings across web proxies and mail gateways to identify clients still reporting Firefox or Thunderbird 137
How to Mitigate CVE-2025-4092
Immediate Actions Required
- Upgrade Firefox to version 138 or later on all managed endpoints
- Upgrade Thunderbird to version 138 or later on all managed workstations
- Enforce automatic updates for Mozilla products through group policy or mobile device management
- Restart browser and mail client processes after patching to ensure the vulnerable code is unloaded from memory
Patch Information
Mozilla resolved CVE-2025-4092 in Firefox 138 and Thunderbird 138. Patch details are published in Mozilla Security Advisory MFSA-2025-28 and Mozilla Security Advisory MFSA-2025-31. Underlying commits are linked from the Mozilla Bug List.
Workarounds
- Restrict browsing to trusted sites and disable JavaScript on untrusted origins until patches are applied
- Configure Thunderbird to display messages as plain text to reduce exposure to HTML rendering paths
- Deploy web filtering to block access to unknown or low-reputation domains from unpatched hosts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
