CVE-2026-121942 in ZBar
Summary
by MITRE • 11/04/2026
ZBar through 0.23.95 contains an out-of-bounds read vulnerability in _zbar_sq_decode() in zbar/sqcode.c that allows attackers to read heap memory outside the image buffer via crafted SQ code images. Attackers can supply an image with a skewed SQ code finder pattern near the edge, producing unchecked sample coordinates that crash the decoder and leak bytes into output.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in ZBar versions up to 0.23.95 represents a critical memory safety flaw within the library's handling of Square Code (SQ) image decoding routines. Specifically located in the _zbar_sq_decode function found in zbar/sqcode.c, this issue stems from insufficient validation of coordinate boundaries when processing specially crafted input images. The root cause lies in the failure to properly check sample coordinates against the allocated heap memory buffer limits before attempting to read data. This lack of bounds checking allows an attacker who can supply a malicious image file to trigger an out-of-bounds read operation, effectively bypassing standard memory protection mechanisms that would otherwise prevent access to unauthorized regions of the process address space.
From a technical perspective, the exploitation vector involves constructing an SQ code image with a skewed finder pattern positioned near the edge of the buffer. When ZBar processes this malformed input, it calculates sample coordinates based on the geometric properties of the detected pattern without verifying that these coordinates fall within the valid range of the allocated memory region. Consequently, the decoder attempts to read data from addresses outside the intended heap allocation. This behavior leads directly to two distinct negative outcomes: a denial of service condition caused by segmentation faults or crashes due to invalid memory access, and potential information disclosure where sensitive bytes from adjacent heap allocations are leaked into the output stream. Such leaks can expose internal application state, cryptographic keys, or other confidential data residing in nearby memory blocks.
The operational impact of this vulnerability is significant for any system relying on ZBar for barcode scanning functionality, particularly those processing untrusted image inputs such as web applications accepting user-uploaded images or mobile apps with camera integration capabilities. An attacker could exploit this flaw to crash the application, disrupting service availability and causing downtime. More critically, the ability to read arbitrary heap memory poses a severe risk of data exfiltration. In complex environments where multiple objects reside in close proximity within the heap, leaking even small amounts of adjacent memory can provide attackers with valuable intelligence about the running process, potentially facilitating further exploitation stages such as return-oriented programming attacks or session hijacking if sensitive tokens are found in nearby buffers.
This vulnerability aligns closely with Common Weakness Enumeration (CWE) category CWE-125, which describes Out-of-bounds Read vulnerabilities where software reads data past the end of a buffer. It also relates to CWE-787, as improper validation leading to memory corruption often precedes more severe exploits like arbitrary code execution in related contexts. In terms of the MITRE ATT&CK framework, this behavior corresponds to techniques involving Memory Scraping or Data from Information Repositories if the leaked data is systematically harvested by an attacker. The attack vector typically falls under Input Validation failures where specific edge cases and malformed inputs are not adequately sanitized before processing.
Mitigation strategies must prioritize immediate patching of the ZBar library to version 0.23.96 or later, which addresses these boundary checks in the decoding logic. For systems unable to update immediately due to dependency constraints, implementing strict input validation at the application layer is essential. This includes verifying image dimensions and content structure before passing them to the decoder, as well as employing sandboxing techniques such as using separate processes with restricted memory permissions for barcode processing tasks. Additionally, enabling compiler-based security features like Address Sanitizer during development can help detect similar issues early in the software lifecycle. Regular auditing of third-party libraries used for image processing is crucial to maintain a robust security posture against these types of low-level memory corruption vulnerabilities.