CVE-2026-49854 in Tornado
Summary
by MITRE • 07/15/2026
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, the optional native extension tornado.speedups implemented websocket_mask without validating that the mask argument is exactly four bytes, allowing the C function to read up to three bytes beyond the provided buffer when reached through Tornado XSRF token decoding with the native extension active. This issue is fixed in version 6.5.6.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/15/2026
The vulnerability resides within the tornado web framework's native extension module known as tornado.speedups which implements certain performance optimizations using C code. This specific flaw manifests during websocket masking operations where the websocket_mask function fails to properly validate that the mask argument supplied contains exactly four bytes as required by the websocket protocol specification. The improper validation allows the C function to read beyond the allocated buffer boundaries, creating a potential memory corruption scenario that could be exploited by malicious actors.
This technical weakness represents a classic buffer overread condition that aligns with CWE-125: Out-of-Bounds Read, where the application accesses memory beyond the intended bounds of a data structure. The vulnerability becomes particularly concerning when combined with Tornado's XSRF token decoding functionality since this pathway activates the native extension and subsequently triggers the unsafe buffer access. The issue occurs because the C implementation assumes a fixed four-byte mask without proper bounds checking, allowing up to three additional bytes to be read from memory that follows the provided buffer.
The operational impact of this vulnerability extends beyond simple memory corruption as it could potentially enable remote code execution or information disclosure depending on how the vulnerable code path is triggered. When Tornado processes XSRF tokens through the native extension, an attacker could craft malicious input that causes the websocket_mask function to read past the intended buffer boundaries, possibly accessing sensitive data from adjacent memory locations or corrupting program state. This type of vulnerability falls under ATT&CK technique T1059.007: Command and Scripting Interpreter: Python, where attackers might leverage such memory corruption to escalate privileges or execute arbitrary code within the application context.
Mitigation strategies should prioritize upgrading to version 6.5.6 or later which includes proper buffer validation in the websocket_mask function. Organizations should also consider disabling the native extension if XSRF token processing is not critical to their application's functionality, as this would prevent the vulnerable code path from being executed. Additionally, implementing proper input validation at the application level and monitoring for unusual memory access patterns can help detect potential exploitation attempts. Security teams should also review their Tornado deployment configurations to ensure that native extensions are only enabled when absolutely necessary and that proper security controls are in place to monitor for buffer overread conditions in other parts of the application stack.