CVE-2025-48172 in CHMLib
Summary
by MITRE • 07/04/2025
CHMLib through 2bef8d0, as used in SumatraPDF and other products, has a chm_lib.c _chm_decompress_block integer overflow. There is a resultant heap-based buffer overflow in _chm_fetch_bytes.
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Analysis
by VulDB Data Team • 07/04/2025
The vulnerability identified as CVE-2025-48172 represents a critical integer overflow flaw within CHMLib version 2bef8d0, which is extensively utilized in SumatraPDF and numerous other software applications. This vulnerability stems from improper handling of decompression operations within the chm_lib.c file, specifically within the _chm_decompress_block function. The flaw manifests when the decompression routine processes malformed compressed data, leading to an integer overflow condition that subsequently triggers a heap-based buffer overflow during the _chm_fetch_bytes operation.
The technical execution of this vulnerability involves a classic integer arithmetic overflow scenario where an unsigned integer operation exceeds its maximum representable value, causing unexpected behavior in subsequent memory allocation calculations. When CHMLib processes compressed help files or chm documents, the _chm_decompress_block function performs calculations to determine buffer sizes needed for decompression operations. The integer overflow occurs during these calculations, resulting in a significantly smaller buffer size than required for the actual decompressed data. This discrepancy creates a heap-based buffer overflow when _chm_fetch_bytes attempts to copy decompressed data into the incorrectly sized buffer, potentially allowing attackers to overwrite adjacent memory regions.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides potential attack vectors for remote code execution within applications that utilize CHMLib for processing chm files. Attackers could craft malicious chm files that trigger the integer overflow condition, potentially leading to arbitrary code execution with the privileges of the affected application. This risk is particularly concerning given CHMLib's widespread adoption in document processing applications, including SumatraPDF, which serves millions of users globally. The vulnerability's exploitation could result in complete system compromise, data exfiltration, or denial of service conditions affecting multiple software platforms.
Mitigation strategies for CVE-2025-48172 should prioritize immediate patching of affected software versions, with particular attention to SumatraPDF and other applications that directly incorporate CHMLib. Organizations should implement network segmentation and file access controls to limit exposure to potentially malicious chm files, while also considering the deployment of application whitelisting solutions to prevent execution of untrusted compressed help files. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and represents a significant concern under ATT&CK technique T1203, Exploitation for Client Execution, as it enables attackers to execute malicious code through compromised document processing applications. Security teams should also consider implementing automated vulnerability scanning tools that can detect and flag the presence of vulnerable CHMLib versions within their software inventory, ensuring comprehensive coverage across all affected applications and systems.