EUVD-2026-41976
GHSA-r4w3-7jp7-m9g5
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L
Local vector and user interaction required as attacker must supply mruby script to interpreter; read-only OOB yields low confidentiality and availability, no integrity impact.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
Lifecycle Timeline
3DescriptionCVE.org
mrubyc through release3.4.1 was found to contain an out-of-bounds read in builtin missing-method lookup inside mrbc_find_method().
AnalysisAI
Out-of-bounds read in mrubyc's builtin method dispatch path (through release3.4.1) allows a local attacker to trigger memory disclosure and interpreter crash by supplying crafted mruby code that invokes a missing method on a builtin class. The flaw resides in mrbc_find_method() in src/class.c, where an off-by-one error in the builtin method table lookup reads one element beyond the valid array boundary. No public exploit code or active exploitation has been identified; EPSS probability stands at 0.15% (5th percentile) and SSVC rates exploitation as none, placing this squarely in low real-world priority territory absent unusual deployment context.
Technical ContextAI
mrubyc is a compact Ruby runtime derived from mruby, purpose-built for microcontrollers and resource-constrained embedded systems. The vulnerable function mrbc_find_method() in src/class.c handles method resolution, including a missing-method fallback path for builtin classes. The upstream fix commit (f83a8b67) reveals the root cause: the function used an off-by-one boundary in what appears to be a binary search over the builtin method table - right was not decremented before the search completed, allowing a read one slot past the end of the array. The removed assert(cls->flag_builtin) line would only have caught the condition in debug builds, leaving release builds silently vulnerable. CWE-125 (Out-of-bounds Read) precisely characterizes this: the read does not corrupt memory but can expose adjacent data or fault on unmapped memory, producing either information disclosure or an availability impact. CPE data in NVD is non-specific ('n/a:n/a'), limiting automated asset detection.
RemediationAI
Apply the upstream fix available in commit f83a8b67ca1c7c62ac0dd548a363d79f767c4e30 (https://github.com/mrubyc/mrubyc/commit/f83a8b67ca1c7c62ac0dd548a363d79f767c4e30); a formally tagged release incorporating this fix has not been independently confirmed, so operators should monitor the mrubyc release page for a version after 3.4.1 or apply the commit patch directly to their build. As a compensating control until a patched release is confirmed, restrict mrubyc to executing only internally authored, statically compiled mruby scripts and prevent any path by which externally controlled input can reach the interpreter - this eliminates the practical attack surface. For embedded product integrators, this control has no runtime performance trade-off but requires application-layer enforcement of script origin. No other vendor advisory URL is available beyond the NVD entry at https://nvd.nist.gov/vuln/detail/CVE-2026-38973.
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Same weakness CWE-125 – Out-of-bounds Read
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today