CVE-2026-2858
Published: 20 February 2026
Summary
CVE-2026-2858 is a medium-severity Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) vulnerability in Wren Wren. Its CVSS base score is 4.8 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 4.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-16 (Memory Protection).
Deeper analysis
CVE-2026-2858 is an out-of-bounds read vulnerability in the Wren programming language implementation, specifically affecting versions up to 0.4.0 of wren-lang/wren. The issue resides in the peekChar function within src/vm/wren_compiler.c, part of the Source File Parser component. Triggered by crafted input, it allows reading beyond allocated memory boundaries, as classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-125 (Out-of-bounds Read). The vulnerability carries a CVSS v3.1 base score of 3.3 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L), indicating low severity primarily due to its local scope and limited impact.
Exploitation requires local access on the target system with low privileges (PR:L), low attack complexity, and no user interaction. A local attacker can provide malicious input to the parser, triggering the out-of-bounds read and potentially causing a denial-of-service condition through application crash or instability, without compromising confidentiality or integrity.
No patches or official mitigations are available, as the wren-lang project was notified early via GitHub issue #1217 but has not responded. A public proof-of-concept exploit is available at https://github.com/oneafter/0122/blob/main/i1217/repro, which security practitioners should review for defensive analysis. Additional details appear in VulDB entries at https://vuldb.com/?ctiid.347097 and https://vuldb.com/?id.347097.
The exploit is publicly available and could be leveraged in targeted local attacks, though no evidence of widespread real-world exploitation has been reported.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7782
Vulnerability details
A vulnerability was identified in wren-lang wren up to 0.4.0. This affects the function peekChar of the file src/vm/wren_compiler.c of the component Source File Parser. Such manipulation leads to out-of-bounds read. The attack needs to be performed locally. The exploit…
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is publicly available and might be used. The project was informed of the problem early through an issue report but has not responded yet.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Out-of-bounds read in Wren parser enables local DoS via crafted input leading to application crash (T1499.004 Application or System Exploitation); no RCE, info leak, or privilege escalation impact per CVSS/description.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly enforces validation of untrusted source input to the Wren parser before peekChar processes it, blocking the crafted local file that triggers the out-of-bounds read.
Applies hardware or OS memory-protection mechanisms that can detect or block the out-of-bounds read performed by peekChar in wren_compiler.c.
Isolates the Wren VM process so that an out-of-bounds read in the parser cannot affect other processes or escalate beyond a single local application crash.