Out-of-Bounds Write in libzvbi Teletext Decoder

Executive Summary

This is an out-of-bounds write vulnerability in libzvbi's Teletext decoder affecting versions up to 0.2.45. It occurs when processing DRCS pixel-mode values in X/28/3 packets. Attackers can send a crafted Teletext stream with every slot set to DRCS_MODE_6_5_4, causing the convert_drcs function to overflow a fixed-size buffer and corrupt memory.

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Detection Guidance

To detect this vulnerability, monitor for crashes in applications using libzvbi 0.2.45 or earlier during Teletext processing. Check logs for segmentation faults or memory corruption errors when handling X/28/3 packets. Use tools like AddressSanitizer to identify out-of-bounds writes in the convert_drcs function.

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Impact Analysis

This vulnerability can cause memory corruption leading to application crashes or potentially arbitrary code execution. It may allow denial of service by crashing the application processing Teletext streams. The impact depends on how libzvbi is used in your system.

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Compliance Impact

This vulnerability primarily affects memory safety and application stability by causing out-of-bounds writes in the Teletext decoder. It does not directly impact compliance with standards like GDPR or HIPAA, which focus on data protection and privacy. However, if exploited, it could lead to denial-of-service conditions or arbitrary code execution, potentially compromising systems handling sensitive data subject to these regulations.

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Mitigation Strategies

Immediately update libzvbi to the latest patched version if available. If not, disable Teletext decoding in affected applications or block untrusted Teletext streams at the network perimeter. Apply strict input validation for DRCS mode values in X/28/3 packets.

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