CVE-2026-111273 in unarr
Summary
by MITRE • 10/16/2026
unarr through 1.1.1 contains an off-by-one heap-based buffer overflow in tar_get_name() in tar/parse-tar.c, reachable through the ar_entry_get_name() API. Attackers can supply a crafted TAR archive with a full ustar prefix and name to write a NUL byte past the allocation, corrupting heap memory and crashing the process.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in unarr versions up to 1.1.1 represents a critical security flaw rooted in improper boundary validation within the TAR archive parsing logic. Specifically, an off-by-one error exists in the tar_get_name function located in the source file tar/parse-tar.c. This function is responsible for extracting and returning the filename from a parsed TAR entry. The vulnerability becomes exploitable when this internal function is invoked through the public ar_entry_get_name API, which serves as the primary interface for applications to retrieve metadata about archive contents. Because unarr is designed to handle various archival formats including AR and TAR, it must robustly parse complex header structures without assuming input integrity. However, in this specific implementation, the code fails to account for the cumulative length of a full ustar prefix combined with the filename itself when allocating memory or validating buffer boundaries.
From a technical perspective, an off-by-one heap-based buffer overflow occurs when a write operation extends one byte beyond the allocated memory region. In the context of TAR archives, particularly those adhering to the POSIX ustar format, filenames can be prefixed with directory paths that are split across multiple header fields. When unarr processes such entries, it calculates the necessary space for the resulting name string but miscalculates by exactly one byte. This miscalculation allows an attacker who supplies a crafted TAR archive containing a carefully constructed full ustar prefix and filename to trigger a write operation that places a NUL byte past the end of the allocated heap buffer. While writing a single null terminator might seem benign, it constitutes memory corruption because it overwrites adjacent data structures on the heap. This corruption can alter control flow variables, metadata associated with other allocations, or critical program state information stored immediately after the target buffer in memory layout.
The operational impact of this vulnerability is significant, primarily manifesting as a denial-of-service condition through process crashes. When the heap memory is corrupted by the out-of-bounds write, the application's internal consistency checks may fail, leading to segmentation faults or abort signals that terminate the unarr process abruptly. For applications relying on unarr for batch processing of archives or integrating archive extraction into larger workflows, such a crash can disrupt services and cause data loss if intermediate states are not persisted safely. Although heap overflows can sometimes be leveraged for arbitrary code execution by manipulating function pointers or vtable entries in adjacent structures, the specific nature of this off-by-one NUL write makes exploitation more challenging but does not eliminate the risk entirely depending on memory allocator behavior and surrounding context. The primary immediate threat remains system instability and service interruption rather than direct remote code execution.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-193, which describes an off-by-one error leading to a buffer overflow that can result in denial of service or potentially other impacts depending on the memory layout. In terms of attack vectors and techniques, this flaw relates to ATT&CK technique T1059, specifically command-line interface abuse if unarr is invoked via scripts, but more accurately reflects aspects of input validation failures often seen in data processing vulnerabilities where malformed inputs trigger unexpected behavior. The lack of rigorous bounds checking during the concatenation or copying of path components highlights a deficiency in secure coding practices regarding string handling and memory allocation limits.
To mitigate this vulnerability, developers must update to patched versions of unarr that correct the boundary calculations within tar_get_name. For users unable to immediately upgrade, implementing input validation at higher-level application layers can help filter out excessively long or malformed archive entries before they reach the parsing engine. Additionally, enabling heap protection mechanisms such as Address Sanitizer during development and testing phases can aid in detecting similar issues early. Organizations should also consider deploying runtime application self-protection tools that monitor for abnormal memory access patterns indicative of buffer overflows. Regular security audits focusing on C/C++ codebases are essential to identify other potential off-by-one errors or improper limit checks in archive parsing libraries, ensuring robust defense against crafted malicious inputs designed to exploit these low-level memory management flaws.