CVE-2026-88344 in flatcc
Summary
by MITRE • 09/22/2026
An out-of-bounds read vulnerability exists in the schema lexer of flatcc 4c3b999e. When an exact-length FlatBuffers schema buffer ends with a digit, the integer digit-scan loop in lex() advances past the end of the input buffer and dereferences the out-of-bounds pointer. A specially crafted schema can trigger a one-byte heap buffer over-read, resulting in application crash and denial of service.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified as CVE-2024-something related to flatcc version 4c3b999e represents a critical memory safety flaw within the schema lexer component. This specific implementation detail involves an out-of-bounds read condition that occurs during the lexical analysis phase of parsing FlatBuffers schemas. The root cause lies in the logic governing integer digit scanning, specifically within the lex function which is responsible for tokenizing numeric values from the input stream. When processing a schema buffer with an exact length boundary where the final character is a digit, the loop designed to consume consecutive digits fails to properly validate its index against the total buffer size before attempting to access the next character. This logical error causes the pointer to advance beyond the allocated memory region, leading to a heap-based out-of-bounds read operation that accesses one byte of unallocated or unrelated memory adjacent to the input buffer.
From a technical perspective, this flaw aligns with CWE-125, which describes an Out-of-Bounds Read vulnerability where software reads data past the end, or before the beginning, of the intended buffer. The specific mechanism here is particularly insidious because it relies on edge-case boundary conditions involving exact-length inputs ending in numeric characters. In many programming languages and environments, reading one byte beyond a heap allocation may not immediately cause a segmentation fault if that memory page happens to be mapped and accessible by the operating system's virtual memory manager. However, the data read is unpredictable and potentially sensitive depending on what resides in adjacent memory regions at runtime. More critically, even if the immediate access does not crash the process due to favorable memory layout conditions, it introduces undefined behavior into the application state. In practice, as noted in reports for this specific version, this often manifests as an application crash because the accessed byte may correspond to unmapped pages or trigger hardware exceptions when used in subsequent logic that expects valid data types derived from the tokenization process.
The operational impact of this vulnerability is primarily a denial of service against applications utilizing flatcc for schema parsing. An attacker who can supply a specially crafted FlatBuffers schema file or network payload containing an exact-length buffer ending with a digit can trigger this out-of-bounds read consistently. The immediate consequence is the termination of the application process, leading to service disruption. In environments where availability is paramount, such as high-throughput data processing pipelines or real-time game networking stacks that rely on FlatBuffers for serialization and deserialization, this vulnerability allows remote attackers to cause persistent downtime without requiring authentication if the schema input source is untrusted. While the primary impact observed is a crash, there are theoretical implications regarding information disclosure if the out-of-bounds read retrieves sensitive data from adjacent heap memory, although exploitation for arbitrary code execution via an out-of-bounds read alone is significantly more complex and less likely than simple denial of service in this context.
This vulnerability maps to MITRE ATT&CK technique T1498.002, Network Denial of Service: Resource Exhaustion through DoS Attack, as the exploitation leads to resource unavailability via process termination. It also relates to CWE-755, Improper Handling of Unexpected or Unusual Input Condition, because the lexer fails to handle a specific but valid input pattern correctly due to insufficient boundary checks. To mitigate this risk, developers must update flatcc to versions where the lex function has been patched with proper bounds checking before accessing subsequent characters in digit-scanning loops. Additionally, defensive coding practices such as using memory-safe languages for critical parsing components or employing static analysis tools that detect out-of-bounds accesses can prevent similar flaws. For immediate remediation without updating the library, input validation should be implemented to ensure schema buffers are processed with explicit length checks before being passed to the lexer, although relying on external wrappers is less robust than fixing the root cause within the parsing engine itself.