CVE-2026-74399 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
evm: terminate and bound the evm_xattrs read buffer
evm_read_xattrs() allocates size + 1 bytes, fills them from the list of enabled xattrs, and then passes strlen(temp) to simple_read_from_buffer(). When no configured xattrs are enabled, the fill loop stores nothing and temp[0] remains uninitialized, so strlen()
reads beyond initialized memory.
Explicitly terminate the buffer after allocation, use snprintf() for each formatted line, and pass the accumulated length, without risk of truncation, to simple_read_from_buffer().
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides in the Linux kernel's extended verification module EVM implementation where improper buffer handling leads to potential information disclosure and system instability. This issue affects the evm_read_xattrs() function which manages the reading of extended attributes for integrity verification purposes. The flaw manifests when the system attempts to read extended attributes but no configured attributes are enabled, creating a scenario where uninitialized memory becomes accessible through improper string length calculation.
The technical root cause involves a classic buffer overrun condition that occurs during the construction of the xattrs read buffer. When evm_read_xattrs() allocates memory using size + 1 bytes for temporary storage, it subsequently fills this buffer with enabled extended attributes. However, when no attributes are configured to be enabled, the fill loop executes without writing any data to the buffer, leaving temp[0] in an uninitialized state. This uninitialized memory is then passed to strlen() function which attempts to read beyond properly initialized memory boundaries, potentially exposing kernel stack contents or other sensitive information.
This vulnerability represents a security risk classified under CWE-126 as "Buffer Over-read" and specifically relates to improper handling of uninitialized memory during buffer operations. The operational impact extends beyond simple information disclosure, as the system may exhibit unpredictable behavior when uninitialized memory values are interpreted as valid string data. Attackers could potentially leverage this condition to extract kernel memory contents, which might reveal sensitive information about kernel structures, memory layout, or other system internals that could aid in further exploitation attempts.
The mitigation strategy addresses the core issue by implementing proper buffer initialization practices and using safer string formatting functions throughout the code path. By explicitly terminating the buffer after allocation, the function ensures that even when no attributes are enabled, the buffer contains predictable and safe initial values. The adoption of snprintf() for each formatted line eliminates the risk of buffer overflow during string construction while maintaining proper null termination. Additionally, passing the accumulated length directly to simple_read_from_buffer() instead of relying on strlen() prevents the read beyond initialized memory condition that was previously present.
This fix aligns with security best practices outlined in the Linux Kernel Security documentation and follows established patterns for safe buffer management in kernel space operations. The solution directly addresses the ATT&CK technique T1068 by preventing unauthorized access to kernel memory through improper buffer handling. The implementation ensures that all paths through the evm_read_xattrs() function maintain proper memory boundaries and prevent information leakage that could compromise system security, particularly in environments where extended verification modules are actively used for integrity monitoring and access control enforcement.