CVE-2026-2858 identifies an out-of-bounds read vulnerability in the wren-lang wren interpreter, affecting versions 0.1 through 0.4.0. The issue resides in the peekChar function within the source file parser (src/vm/wren_compiler.c), where improper bounds checking allows reading memory outside the allocated buffer. This vulnerability can be triggered by a local attacker with limited privileges, requiring no user interaction or elevated permissions beyond local access. The out-of-bounds read could lead to disclosure of sensitive memory contents, potentially leaking information useful for further attacks or debugging sensitive data. The vulnerability does not directly allow code execution or privilege escalation but poses confidentiality risks. The exploit code is publicly available, increasing the risk of exploitation in environments where wren-lang is used locally. The wren-lang project has been informed but has not yet responded or released a patch. The CVSS 4.0 vector indicates low attack complexity and no user interaction, but limited scope and impact, resulting in a medium severity rating. This vulnerability primarily affects developers and systems embedding wren-lang for scripting or automation tasks.

The primary impact of CVE-2026-2858 is the potential disclosure of sensitive information due to out-of-bounds memory reads. While it does not allow remote exploitation or privilege escalation, local attackers with limited access can leverage this flaw to gain insights into memory contents, which may include sensitive data or internal program state. This can aid in further attacks, debugging, or reverse engineering efforts. Organizations using wren-lang in development environments, embedded systems, or automation scripts may face confidentiality risks. Although the vulnerability does not directly affect system availability or integrity, the exposure of sensitive data could lead to indirect impacts such as intellectual property theft or aiding attackers in crafting more sophisticated exploits. The medium severity reflects the limited attack vector and scope but acknowledges the risk posed by publicly available exploits.

Until an official patch is released by the wren-lang project, organizations should implement the following mitigations: 1) Restrict local access to systems running wren-lang to trusted users only, minimizing the risk of local exploitation. 2) Monitor and audit usage of wren-lang interpreters to detect unusual or unauthorized activity. 3) Employ memory protection mechanisms such as address space layout randomization (ASLR) and data execution prevention (DEP) to reduce exploitation impact. 4) Consider sandboxing or containerizing wren-lang execution environments to limit potential data exposure. 5) Review and limit the use of wren-lang in production or sensitive environments until a patch is available. 6) Stay updated with wren-lang project communications for forthcoming patches and apply them promptly once released. 7) Conduct code reviews and static analysis on scripts or modules using wren-lang to identify potential abuse vectors. These steps go beyond generic advice by focusing on access control, monitoring, and environment hardening specific to this local out-of-bounds read vulnerability.