CVE-2026-4111 in libarchive
Summary
by MITRE • 03/13/2026
A flaw was identified in the RAR5 archive decompression logic of the libarchive library, specifically within the archive_read_data() processing path. When a specially crafted RAR5 archive is processed, the decompression routine may enter a state where internal logic prevents forward progress. This condition results in an infinite loop that continuously consumes CPU resources. Because the archive passes checksum validation and appears structurally valid, affected applications cannot detect the issue before processing. This can allow attackers to cause persistent denial-of-service conditions in services that automatically process archives.
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Analysis
by VulDB Data Team • 04/29/2026
The vulnerability CVE-2026-4111 represents a critical denial-of-service flaw within the libarchive library's RAR5 decompression implementation. This issue manifests specifically within the archive_read_data() function's processing path, where maliciously crafted RAR5 archives can trigger a condition that prevents normal decompression progress. The flaw operates at the intersection of archive processing logic and resource management, creating a scenario where legitimate decompression routines become trapped in perpetual execution cycles without advancing through the archive data structure. The vulnerability affects systems that rely on libarchive for automatic archive processing, particularly those handling untrusted inputs from external sources.
The technical root cause of this vulnerability stems from inadequate state management within the RAR5 decompression algorithm implementation. When processing malformed RAR5 archives, the decompression routine enters a condition where internal loop control mechanisms fail to advance the processing pointer, causing the decompression engine to repeatedly execute the same logical steps without consuming new data. This condition is particularly insidious because it occurs after initial checksum validation and structural parsing have completed successfully, meaning that applications cannot detect the malformed archive state before initiating the problematic decompression sequence. The flaw is categorized under CWE-835, which addresses infinite loops in software implementations, specifically where loop termination conditions are not properly enforced or validated.
From an operational impact perspective, this vulnerability enables attackers to create persistent denial-of-service conditions in services that automatically process archive files. Systems utilizing libarchive for tasks such as email attachment processing, file upload validation, automated backup systems, or content delivery networks become vulnerable to resource exhaustion attacks. The infinite loop consumes CPU cycles continuously without producing meaningful output, effectively rendering the affected service unavailable to legitimate users. This vulnerability can be exploited through various attack vectors including web applications accepting file uploads, automated processing pipelines, or any system that automatically decompresses user-provided archives without proper input validation. The impact extends beyond simple service disruption to potentially affecting system availability and resource allocation across networked environments.
Mitigation strategies for CVE-2026-4111 should focus on immediate patching of affected libarchive versions, implementing input validation and timeout mechanisms, and establishing proper resource limits for decompression processes. Organizations should deploy updated libarchive libraries that contain corrected decompression logic and ensure that applications using the library implement appropriate timeout configurations to prevent indefinite processing. Network-based protections can include implementing file type filtering and content scanning before archive processing, while application-level defenses should incorporate memory and CPU usage monitoring to detect anomalous processing patterns. The vulnerability aligns with ATT&CK technique T1499.004, which covers resource exhaustion attacks, and represents a classic example of how decompression vulnerabilities can be weaponized for denial-of-service purposes in software systems processing untrusted data inputs.