CVE-2026-52131 in llama.cpp
Summary
by MITRE • 09/01/2026
llama.cpp b5693 and before has a Reachable Assertion via the gguf_reader::read function.
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Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified in llama.cpp prior to build version b5693 represents a critical reliability issue stemming from improper input validation within the GGUF model file reader component. The specific flaw resides in the gguf_reader::read function, which is responsible for parsing and interpreting the binary structure of GGUF files used by various large language models. When processing malformed or unexpectedly structured data, this function fails to adequately check boundary conditions or type consistency before proceeding with memory operations or logical assertions. This lack of robust defensive programming allows an attacker who can supply a crafted input file to trigger a reachable assertion failure within the application runtime environment.
From a technical perspective, this issue aligns closely with CWE-617, which describes Reachable Assertion failures where code relies on assumptions about program state that are not guaranteed by external inputs. In the context of llama.cpp, an assertion is typically used as a debugging aid to catch internal logic errors during development or testing phases. However, when such assertions remain enabled in production builds or are triggered by externally supplied data, they result in immediate application termination rather than graceful error handling. This behavior indicates that the software does not implement proper exception handling or input sanitization mechanisms for untrusted model files, leaving it vulnerable to denial of service attacks through simple file-based triggers.
The operational impact of this vulnerability is primarily centered on availability and system stability. Since llama.cpp is often deployed in server environments or automated pipelines where large language models are processed continuously, a crash caused by a malformed GGUF file can disrupt services for multiple users. An adversary could exploit this weakness by distributing maliciously crafted model files that appear valid but contain subtle structural anomalies designed to hit the assertion condition. Upon loading such a file, the application would abort execution abruptly, leading to service downtime and potential data loss if state was not properly persisted before the crash occurred. This is particularly concerning in scenarios where automated systems ingest models from third-party repositories without rigorous pre-validation checks.
This vulnerability can be mapped to specific entries within established security frameworks. It corresponds to CWE-20 Improper Input Validation, as the root cause is the failure to verify that incoming data meets expected structural constraints before processing. Furthermore, it relates to ATT&CK technique T1496 Resource Hijacking under the sub-technique of Denial of Service via resource exhaustion or application crash, although in this specific case, the mechanism is a direct assertion fault rather than computational overload. The lack of robust error recovery mechanisms also touches upon CWE-755 Improper Handling of Unexpected Exceptional Conditions, highlighting gaps in how the software manages abnormal states during file parsing operations.
To mitigate this risk, developers and users should immediately upgrade to version b5693 or later where these assertion checks have been addressed with proper input validation logic. For environments that cannot be updated instantly, it is advisable to implement strict sandboxing for any model files received from untrusted sources. Additionally, integrating static analysis tools into the CI/CD pipeline can help detect similar patterns of unchecked assumptions in future code changes. Security teams should also consider deploying runtime application self-protection (RASP) solutions or monitoring agents that can detect abnormal process terminations and automatically restart services to minimize downtime while longer-term fixes are implemented.