CVE-2026-64306 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
crypto: drbg - Fix returning success on failure in CTR_DRBG
drbg_ctr_generate() sometimes returns success when it fails, leaving the output buffer uninitialized. Fix it.
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability identified in the Linux kernel's crypto subsystem represents a critical flaw in the deterministic random bit generator implementation known as CTR_DRBG. This issue affects the drbg_ctr_generate() function which is responsible for generating cryptographically secure random numbers using the Counter mode Deterministic Random Bit Generator algorithm. The problem manifests when the function encounters an error condition during the generation process yet incorrectly returns a success status code instead of indicating failure. This erroneous behavior creates a dangerous scenario where callers of the function believe random number generation succeeded when it actually failed, resulting in the output buffer remaining uninitialized and potentially containing garbage data or sensitive information from previous operations.
The technical root cause of this vulnerability lies in the improper error handling within the CTR_DRBG implementation where error conditions are not properly propagated back to the calling functions. When cryptographic algorithms fail during their execution, they must consistently return appropriate error codes to ensure that downstream components can react appropriately and avoid using potentially compromised or invalid output data. In this case, the function fails to check whether the underlying cryptographic operations within the counter mode DRBG have completed successfully before returning control to the caller. The vulnerability specifically impacts the deterministic random bit generator's ability to maintain cryptographic security guarantees by allowing failed operations to masquerade as successful ones, creating a potential vector for attacks that exploit uninitialized memory contents.
The operational impact of this vulnerability extends beyond simple incorrect functionality as it fundamentally undermines the trustworthiness of random number generation within the Linux kernel. Applications and system components that rely on cryptographically secure random numbers for security purposes such as key generation, nonce creation, session identifiers, or cryptographic protocol operations may be exposed to serious security risks. An attacker could potentially exploit this vulnerability by crafting inputs that trigger the error condition in drbg_ctr_generate() while simultaneously monitoring for cases where uninitialized data is used, thereby gaining information about system memory state or potentially predicting cryptographic outputs. This flaw directly violates the principle of fail-secure behavior expected from cryptographic implementations and represents a significant weakening of the kernel's security posture.
This vulnerability maps to CWE-252, which describes "Unchecked Return Value" in software security practices, where functions that should return error codes are not properly validated by callers, leading to potentially dangerous states. The issue also relates to ATT&CK technique T1083, which involves discovering system information through the use of commands like /proc and memory inspection that could be leveraged to exploit uninitialized buffer contents. The fix for this vulnerability requires implementing proper error code checking within the drbg_ctr_generate() function to ensure that when cryptographic operations fail, appropriate error codes are returned rather than allowing success codes to be returned in failure scenarios. System administrators should update their kernels to versions containing this fix and review applications that depend on kernel random number generation for potential exposure to uninitialized data usage patterns.
The broader implications of this vulnerability highlight the critical importance of proper error handling in cryptographic implementations, where even seemingly minor flaws can have significant security consequences. Cryptographic libraries and kernel subsystems must maintain rigorous validation of all operations and ensure that failure conditions are properly communicated to calling functions to prevent downstream components from operating on invalid data. This fix demonstrates the necessity of thorough testing and code review processes specifically focused on error handling pathways within security-critical code sections, as uninitialized memory access represents one of the most common categories of vulnerabilities in cryptographic implementations and system software.