Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-4424 is a heap buffer overflow and information leak vulnerability in libarchive's RAR3 extraction code. It occurs due to improper handling of the LZSS sliding window size after processing a PPMd-compressed block. Specifically, when transitioning between compression methods, the code fails to reallocate the LZSS window buffer to match the new dictionary size, causing a mismatch between the buffer size and the expected size."}, {'type': 'paragraph', 'content': 'This mismatch leads to an out-of-bounds read in the function copy_from_lzss_window(), where the code attempts to copy more data than the allocated buffer size, leaking sensitive heap memory. The leaked data is returned before CRC integrity checks are performed, allowing attackers to reliably read arbitrary heap contents from a specially crafted RAR archive without authentication or user interaction.'}, {'type': 'paragraph', 'content': 'The vulnerability arises from a sequence of bugs including dictionary size inflation, faulty allocation guards, out-of-bounds reads, incorrect filter validation, and late CRC checks. The issue can be triggered by a crafted 170-byte RAR3 archive, leaking approximately 257 bytes of heap memory.'}] [1, 2]

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Impact Analysis

This vulnerability can lead to the disclosure of sensitive heap memory information on systems using libarchive to process RAR archives. An attacker can exploit it remotely by providing a specially crafted RAR archive, causing the application to leak heap contents without requiring authentication or user interaction.

The leaked heap data may contain sensitive information, potentially exposing confidential data or internal application state. Since the leak occurs before CRC integrity checks, the attacker can reliably obtain this information, which could be used for further attacks or information gathering.

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Compliance Impact

I don't know

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Detection Guidance

This vulnerability involves a heap out-of-bounds read triggered by processing specially crafted RAR archives with libarchive. Detection can focus on monitoring for suspicious or malformed RAR archive files being processed by applications using libarchive, especially those that automatically extract RAR files.

Since the vulnerability causes libarchive to leak heap memory during extraction before CRC checks, one detection approach is to analyze logs or outputs of archive extraction tools for unexpected memory disclosures or errors related to RAR file processing.

There are no explicit commands provided in the resources for direct detection of this vulnerability on a system or network.

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Mitigation Strategies

To mitigate this vulnerability, the primary step is to update libarchive to a version that includes the fix for CVE-2026-4424.

The fix involves proper reallocation of the LZSS window buffer, defensive bounds checking to prevent out-of-bounds reads, and correct validation of filter block lengths, eliminating the information leak.

Until an updated libarchive version is deployed, avoid processing untrusted or suspicious RAR archives, especially those received from unverified sources.

If possible, disable automatic extraction of RAR archives in applications or services that use libarchive to prevent exploitation.

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