ZBar Out-of-Bounds Read in SQ Code Decoder

Executive Summary

CVE-2026-121942 is an out-of-bounds read vulnerability in ZBar's SQ code decoder. It occurs in the _zbar_sq_decode() function where pixel sampling coordinates are calculated without proper bounds checking. When processing a crafted image with a skewed SQ code near the edge, the interpolation formula can produce coordinates outside the image buffer. These invalid coordinates are then used to read heap memory, potentially crashing the decoder and leaking sensitive data.

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Detection Guidance

To detect this vulnerability, scan systems running ZBar versions up to 0.23.95 for crashes or memory leaks when processing SQ code images. Use tools like zbarcam or zbarimg with crafted test images containing skewed SQ codes near edges. Monitor for segmentation faults or unexpected output during image decoding.

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Impact Analysis

This vulnerability allows attackers to read heap memory outside the intended image buffer by supplying a maliciously crafted SQ code image. This could lead to application crashes, information disclosure, or potential privilege escalation if sensitive data is leaked. The impact depends on how ZBar is used in your system.

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Compliance Impact

This vulnerability could impact compliance by potentially exposing sensitive data through memory leaks. GDPR requires protecting personal data, and HIPAA mandates safeguarding protected health information. If exploited, this flaw might lead to unauthorized data exposure, violating these regulations and requiring breach notifications.

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Mitigation Strategies

Immediately upgrade ZBar to the latest version beyond 0.23.95, as patches address the bounds checking issue. If upgrading is not possible, disable SQ code decoding in applications using ZBar or restrict image processing to trusted sources. Apply input validation for images containing SQ codes.

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