CVE-2026-92027 Overview
CVE-2026-92027 is a use-after-free vulnerability [CWE-416] in the DOM: Streams component of Mozilla Firefox and Thunderbird. The flaw affects how the Streams implementation manages object lifetimes within the Document Object Model (DOM). An attacker who convinces a user to load a crafted web page can trigger memory corruption that may lead to arbitrary code execution in the browser process.
Mozilla addressed the issue across multiple release trains, including Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.
Critical Impact
Successful exploitation can result in arbitrary code execution within the browser or mail client renderer, compromising confidentiality, integrity, and availability of the affected system.
Affected Products
- Mozilla Firefox versions prior to 156
- Mozilla Firefox ESR versions prior to 115.41, 140.16, and 153.3
- Mozilla Thunderbird versions prior to 156, 140.16, and 153.3
Discovery Timeline
- 2026-09-15 - CVE-2026-92027 published to the National Vulnerability Database (NVD)
- 2026-09-18 - Last updated in NVD database
Technical Details for CVE-2026-92027
Vulnerability Analysis
The vulnerability resides in the DOM Streams implementation, which provides the JavaScript Streams API used for processing readable, writable, and transform streams. A use-after-free occurs when the code continues to reference a memory region that has already been deallocated. Attackers can groom the heap to place attacker-controlled data in the freed region, gaining influence over subsequent operations.
Because the affected component executes untrusted script through standard web content, exploitation only requires a target to visit a malicious page or preview a crafted HTML email. In Thunderbird, script execution in mail is disabled by default, but the same shared rendering code path is present.
Root Cause
The root cause is improper object lifetime management within the DOM: Streams component. Reference counts or ownership assumptions are violated during specific stream state transitions, allowing a JavaScript-reachable object to reference freed backing memory. This class of defect maps to CWE-416: Use After Free.
Attack Vector
Exploitation is network-based and requires user interaction. An attacker hosts a malicious web page that uses the Streams API in a manner that triggers the freed-object condition, then coerces the browser to reuse the reclaimed allocation. The resulting memory corruption can be leveraged to escape sandboxing controls when combined with additional vulnerabilities.
No public proof-of-concept exploit code has been released. See Mozilla Bug Report #2068433 and Mozilla Security Advisory MFSA-2026-90 for vendor-provided technical context.
Detection Methods for CVE-2026-92027
Indicators of Compromise
- Unexpected Firefox or Thunderbird process crashes with signatures referencing DOM Streams objects or mozilla::dom::ReadableStream frames
- Child renderer processes spawning unusual child processes such as command shells or scripting hosts
- Outbound network connections from firefox.exe or thunderbird.exe to newly registered or low-reputation domains following page loads
Detection Strategies
- Monitor endpoint telemetry for anomalous child-process creation from browser and mail client binaries
- Correlate browser crash reports with recently visited URLs to identify potential exploitation attempts
- Deploy behavioral analytics that flag memory corruption patterns such as heap grooming followed by shellcode-style allocations
Monitoring Recommendations
- Track installed browser and mail client versions across the fleet and alert on hosts running unpatched builds
- Ingest browser crash and telemetry data into a centralized SIEM for correlation with web proxy logs
- Alert on execution of untrusted binaries written to user profile directories used by Firefox or Thunderbird
How to Mitigate CVE-2026-92027
Immediate Actions Required
- Upgrade Firefox to version 156 or later on all managed endpoints
- Upgrade Firefox ESR deployments to 115.41, 140.16, or 153.3 depending on the deployed channel
- Upgrade Thunderbird to version 156, 140.16, or 153.3 as appropriate for the deployed release train
- Restart affected applications after patching to ensure the new binaries load in memory
Patch Information
Mozilla released fixes across the Firefox and Thunderbird release channels. Consult the vendor advisories for the corresponding channel: MFSA-2026-90, MFSA-2026-91, MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96.
Workarounds
- Enforce enterprise policies that disable JavaScript execution on untrusted origins until patches are deployed
- Ensure Thunderbird retains its default setting that blocks scripting in mail content
- Restrict browser usage on high-value systems to allowlisted internal applications while patch rollouts complete
- Enable automatic updates through enterprise deployment tooling to shorten future exposure windows
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
