CVE-2018-5996 in 7-zip
Summary
by MITRE
Insufficient exception handling in the method NCompress::NRar3::CDecoder::Code of 7-Zip before 18.00 and p7zip can lead to multiple memory corruptions within the PPMd code, allows remote attackers to cause a denial of service (segmentation fault) or execute arbitrary code via a crafted RAR archive.
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Analysis
by VulDB Data Team • 01/10/2025
The vulnerability identified as CVE-2018-5996 represents a critical security flaw within the 7-Zip compression utility and its associated p7zip implementation. This issue manifests in the NCompress::NRar3::CDecoder::Code method where inadequate exception handling mechanisms exist, creating a pathway for malicious actors to exploit memory corruption vulnerabilities. The flaw specifically affects versions prior to 7-Zip 18.00 and p7zip, making a substantial portion of deployed systems susceptible to exploitation. The vulnerability resides within the PPMd (Prediction by Partial Matching) code module which is responsible for decompressing RAR archives, particularly those with complex compression structures. When processing malformed or crafted RAR archives, the insufficient exception handling causes the application to fail in properly managing memory allocation and deallocation sequences, leading to unpredictable behavior.
The technical exploitation of this vulnerability occurs through the manipulation of RAR archive structures that trigger memory corruption during decompression operations. The PPMd code's failure to properly validate input data and handle exceptional conditions results in buffer overflows, use-after-free scenarios, and other memory corruption patterns that can be leveraged by remote attackers. This flaw operates at a low level within the decompression pipeline where the decoder attempts to reconstruct compressed data streams, and the lack of proper error boundaries allows malicious input to cascade into system-level memory corruption. The vulnerability's impact is amplified by the widespread use of 7-Zip across multiple operating systems and platforms, including windows, linux, and unix variants, making it an attractive target for attackers seeking to compromise diverse computing environments.
The operational consequences of CVE-2018-5996 extend beyond simple denial of service conditions to encompass full arbitrary code execution capabilities. Attackers can craft malicious RAR archives that, when processed by vulnerable 7-Zip implementations, trigger segmentation faults or cause the application to execute unintended code sequences. This capability allows for privilege escalation scenarios where attackers can gain control over the victim system, potentially leading to complete system compromise. The vulnerability's remote exploitation nature means that simply opening or processing a malicious archive can result in system compromise, making it particularly dangerous in environments where automated archive processing occurs. The impact affects both server and client systems, with enterprise environments particularly vulnerable due to the extensive use of archive processing in backup systems, software distribution, and automated deployment pipelines.
Mitigation strategies for CVE-2018-5996 primarily focus on immediate software updates to versions 18.00 or later where the exception handling has been properly implemented. System administrators should prioritize patching all affected 7-Zip installations and ensure that p7zip implementations are updated to versions that address the memory corruption issues within the PPMd code. Network segmentation and access controls should be implemented to limit exposure to potentially malicious archives, particularly in automated processing environments. Input validation mechanisms should be strengthened to reject suspicious archive structures before they reach the decompression engine. The vulnerability aligns with CWE-704 (Incorrect Type Conversion or Cast) and CWE-707 (Improper Neutralization of Input During Web Page Generation) categories, while also mapping to ATT&CK techniques involving privilege escalation and code execution through software exploitation. Organizations should implement monitoring solutions to detect attempts to process suspicious archive files and establish incident response procedures for handling potential exploitation attempts. Regular security assessments of archive processing workflows and comprehensive vulnerability scanning should be conducted to identify any remaining instances of vulnerable software deployments.