CVE-2026-2657: 
Homebrew vulnerability analysis and mitigation

CVE-2026-2657 is a stack-based buffer overflow vulnerability in the printError function of the Wren scripting language compiler (src/vm/wren_compiler.c), affecting wren-lang/wren versions up to and including 0.4.0. The flaw was reported via a GitHub issue on January 22, 2026, and publicly disclosed on February 18, 2026. It carries a CVSS v3.1 base score of 5.5 (Medium), requiring local access and low privileges to exploit (Feedly, GitHub Issue).

The root cause is improper use of the unsafe vsprintf function in the printError function (line 432 of src/vm/wren_compiler.c), which writes a formatted error message into a fixed-size stack buffer (approximately 159 bytes) without bounds checking — classified as CWE-121 (Stack-based Buffer Overflow) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). When a Wren script triggers a compilation error with a sufficiently long method name or format argument (e.g., via declareMethod), vsprintf writes past the buffer boundary, corrupting the stack. Exploitation requires local access and the ability to supply a crafted Wren script to the interpreter; a public proof-of-concept reproducer file and harness code are available (GitHub Issue, PoC Repo).

Successful exploitation causes a denial of service via application crash (stack corruption leading to abort), with no impact on confidentiality or data integrity. The vulnerability is limited in scope to the availability of the Wren VM process; it does not enable remote code execution, privilege escalation, or data exfiltration based on current analysis. Applications embedding the Wren scripting engine and processing untrusted scripts are most at risk (Feedly, GitHub Issue).

A public proof-of-concept exploit (a crafted Wren script reproducer) is available on GitHub, and the ASAN-confirmed crash was demonstrated on Linux x86_64 in release mode. There is no evidence of in-the-wild exploitation at this time, and the vulnerability has not been added to the CISA Known Exploited Vulnerabilities catalog. The EPSS score is approximately 0.013% (0.000130), reflecting low probability of active exploitation. The project maintainers had not responded to the issue report as of the disclosure date (Feedly, PoC Repo).

1. Prepare environment: Obtain a local system with wren-lang/wren version 0.4.0 or earlier installed, or build from source with the vulnerable version.
2. Craft malicious Wren script: Create a Wren source file containing a class definition with an excessively long method name (e.g., class Teskkkk...t { Nys(.prin{t(7H%©m...) designed to trigger a compilation error with a format string argument exceeding the 159-byte stack buffer in printError.
3. Execute the script: Pass the crafted file to the Wren interpreter or any application embedding the Wren VM (e.g., ./bin/harness repro using the published harness code).
4. Trigger overflow: The compiler's declareMethod function calls error, which calls printError; vsprintf writes the oversized error message past the stack buffer boundary, corrupting the stack and causing the process to abort.
5. Observe crash: The application crashes with a stack-buffer-overflow, achieving denial of service. With ASAN enabled, the crash is confirmed at wren_compiler.c:432 (GitHub Issue, PoC Repo).

• Process: Unexpected crash or abort of the Wren VM process or any application embedding Wren; ASAN output referencing stack-buffer-overflow in printError / vsprintf at wren_compiler.c:432.
• Logs: Application logs showing abrupt termination during Wren script compilation, particularly when processing class or method definitions; error messages referencing declareMethod or wrenCompile.
• File System: Presence of unusual or malformed .wren script files with excessively long class/method names submitted to the interpreter.
• Core Dumps: Core dump files generated by the Wren host process, with stack traces pointing to vsprintf, printError, error, declareMethod, and wrenInterpret (GitHub Issue).

The Feedly data indicates a patch is available; organizations should upgrade wren-lang/wren from version 0.4.0 or earlier to the latest patched release as the primary remediation. As a workaround, restrict local system access so that only trusted users can supply scripts to the Wren interpreter, and avoid processing untrusted Wren source files with vulnerable versions. Monitor for unexpected application crashes that may indicate exploitation attempts. The upstream project had not formally responded to the issue report at the time of disclosure, so users should monitor the wren-lang/wren GitHub repository for official patch releases (Feedly, GitHub Issue).

Red Hat has tracked this CVE in their security advisory database, though no specific Red Hat products are listed as affected. No significant public researcher commentary, vendor statements, or media coverage beyond standard vulnerability database aggregation has been identified for this vulnerability (Red Hat Advisory).