CVE-2026-74391 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing: Bound synthetic-field strings with seq_buf
The synthetic field helpers build a prefixed synthetic variable name and a generated hist command in fixed MAX_FILTER_STR_VAL buffers. The current code appends those strings with raw strcat(), so long key lists, field names, or saved filters can run past the end of the staging buffers.
Build both strings with seq_buf and propagate -E2BIG if either the synthetic variable name or the generated command exceeds MAX_FILTER_STR_VAL. This keeps the existing tracing-side limit while using the helper intended for bounded command construction.
[ sdr: Moved struct seq_buf *s for upside-down x-mas tree formatting ]
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability resides within the Linux kernel's tracing subsystem where synthetic field helpers are responsible for constructing prefixed variable names and generated hist commands using fixed-size buffers of MAX_FILTER_STR_VAL capacity. The flaw manifests through improper string handling mechanisms that rely on raw strcat() operations instead of bounded buffer management. When processing lengthy key lists, field names, or saved filters, the unbounded string concatenation can overflow these predetermined staging buffers leading to potential memory corruption and system instability.
The technical implementation issue stems from the absence of proper bounds checking during string construction processes within the tracing framework. The synthetic field helpers operate under the assumption that all generated strings will remain within acceptable size limits, but this assumption fails when dealing with complex or extended input data. This vulnerability directly relates to CWE-121 as it involves stack-based buffer overflow conditions where concatenated strings exceed allocated buffer boundaries. The implementation lacks proper validation mechanisms to ensure string length constraints are maintained throughout the construction process.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation and system compromise within kernel space. Attackers could exploit this weakness by crafting malicious tracing events with excessively long field names or key lists that trigger buffer overflows during synthetic field generation. This creates opportunities for denial-of-service conditions or more severe exploitation scenarios where corrupted kernel memory could be manipulated to execute arbitrary code with kernel privileges. The vulnerability affects systems heavily reliant on kernel tracing capabilities and could impact security monitoring solutions that depend on synthetic field processing.
Mitigation strategies should focus on implementing proper bounded buffer management through the seq_buf infrastructure as recommended in the fix. The solution involves replacing raw string concatenation operations with sequence buffer handling that automatically enforces size limits and returns appropriate error codes when boundaries are exceeded. This approach aligns with ATT&CK technique T1059 by preventing command injection scenarios that could occur through malformed tracing data. System administrators should ensure kernel updates are applied promptly to address this vulnerability, while also monitoring for unusual tracing behavior or memory allocation errors that might indicate exploitation attempts.
The fix demonstrates proper defensive programming practices by utilizing established kernel infrastructure designed specifically for bounded string operations. The seq_buf implementation provides automatic size management and error propagation mechanisms that prevent buffer overflows while maintaining compatibility with existing tracing functionality. This approach ensures that the existing MAX_FILTER_STR_VAL limit remains effective while providing robust protection against excessive string growth during synthetic field construction. The solution also addresses potential issues related to upside-down x-mas tree formatting through proper struct seq_buf *s handling, ensuring clean code structure and maintainability of the tracing subsystem.