CVE-2026-31988 in yauzl
Summary
by MITRE • 03/12/2026
yauzl (aka Yet Another Unzip Library) version 3.2.0 for Node.js contains an off-by-one error in the NTFS extended timestamp extra field parser within the getLastModDate() function. The while loop condition checks cursor < data.length + 4 instead of cursor + 4 <= data.length, allowing readUInt16LE() to read past the buffer boundary. A remote attacker can cause a denial of service (process crash via ERR_OUT_OF_RANGE exception) by sending a crafted zip file with a malformed NTFS extra field. This affects any Node.js application that processes zip file uploads and calls entry.getLastModDate() on parsed entries. Fixed in version 3.2.1.
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Analysis
by VulDB Data Team • 03/17/2026
The vulnerability identified as CVE-2026-31988 resides within the yauzl library, a popular Node.js module used for parsing zip files. This library serves as a foundational component in numerous applications that handle file decompression, making it a critical element in the Node.js ecosystem. The flaw manifests in the NTFS extended timestamp extra field parser within the getLastModDate() function, where an off-by-one error creates a dangerous buffer boundary condition. The technical implementation contains a loop condition that incorrectly evaluates cursor < data.length + 4 rather than the correct cursor + 4 <= data.length, creating a scenario where memory access extends beyond intended boundaries.
The operational impact of this vulnerability extends beyond simple code execution issues, as it represents a classic buffer over-read condition that can lead to process termination through ERR_OUT_OF_RANGE exceptions. When a remote attacker crafts a malicious zip file containing a malformed NTFS extra field, the library's parser attempts to read beyond the allocated buffer space, triggering a crash in any Node.js application that processes such files and subsequently calls the getLastModDate() method on parsed entries. This vulnerability directly affects the availability aspect of the application's security posture, as legitimate users could experience service disruption through crafted zip file uploads.
The flaw demonstrates characteristics consistent with CWE-129, which addresses improper validation of buffer limits, and aligns with ATT&CK technique T1203 for exploitation of input validation vulnerabilities. The vulnerability's exploitation requires minimal sophistication, as it only necessitates crafting a specific zip file structure rather than complex code manipulation. Applications utilizing yauzl for zip file processing, particularly those accepting user uploads, face significant risk exposure. The fix implemented in version 3.2.1 addresses the core issue by correcting the boundary condition in the while loop, ensuring proper validation before buffer access occurs. Security practitioners should prioritize updating affected applications to version 3.2.1 or later, as this represents a critical patch for maintaining application stability and preventing denial of service attacks through crafted zip file inputs. The vulnerability underscores the importance of proper buffer management in file parsing libraries and demonstrates how seemingly minor boundary condition errors can create significant availability risks in widely-used components.