CVE-2021-35331 in TCL
Summary
by MITRE • 07/05/2021
** DISPUTED ** In Tcl 8.6.11, a format string vulnerability in nmakehlp.c might allow code execution via a crated file. NOTE: multiple third parties dispute the significance of this finding.
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Analysis
by VulDB Data Team • 08/04/2024
The vulnerability identified as CVE-2021-35331 relates to a format string vulnerability discovered in Tcl version 8.6.11 within the nmakehlp.c source file. This type of vulnerability falls under the category of CWE-134 which specifically addresses the use of format strings without proper validation or sanitization. The nmakehlp.c component serves as a helper utility for the nmake build system integration within Tcl's build process, making it a critical element in the software development lifecycle for Tcl applications.
The technical flaw manifests when the nmakehlp.c code processes user-supplied input through format string functions without adequate input validation. This creates an opportunity for attackers to inject malicious format specifiers that can lead to arbitrary code execution. The vulnerability is particularly concerning because it occurs during the build process when a crafted file is created, potentially allowing remote attackers to execute arbitrary code on systems where Tcl is used for development or build operations. The format string vulnerability enables attackers to manipulate memory layout, read from arbitrary memory locations, and potentially overwrite critical function pointers or return addresses.
The operational impact of this vulnerability extends beyond simple code execution as it affects the integrity of the build environment itself. When developers or automated systems process a maliciously crafted file through Tcl's build tools, the attacker can leverage this vulnerability to gain unauthorized access to the build system. This represents a significant risk in continuous integration environments where automated builds are performed, as it could allow attackers to inject malicious code into the build pipeline or compromise the integrity of compiled binaries. The vulnerability's exploitation potential is amplified by the fact that it can be triggered during normal development workflows when developers use Tcl-based build tools.
Security practitioners should approach this vulnerability with caution given the disputed nature of the finding as noted in the CVE description. However, the potential implications remain significant for organizations using Tcl 8.6.11 in their development environments. The recommended mitigation strategies include upgrading to a patched version of Tcl where available, implementing strict input validation for files processed by nmakehlp.c, and conducting thorough code reviews of build processes to identify potential format string usage patterns. Organizations should also consider implementing runtime protections such as stack canaries and address space layout randomization to reduce the exploitation success rate. From an ATT&CK framework perspective, this vulnerability maps to techniques involving execution through development tools and supply chain compromises, as it targets the build infrastructure rather than runtime execution environments. The vulnerability highlights the importance of securing development toolchains as part of overall security posture, since compromised build systems can lead to persistent backdoors in deployed applications.