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CVE-2025-39789 is a security vulnerability identified within the Linux kernel’s cryptographic subsystem, specifically affecting the x86 AEGIS implementation.
The issue originates in the handling of memory allocation routines during cryptographic operations involving the skcipher_walk interface.
When the kernel executes symmetric cipher walkthroughs, it occasionally requires dynamic memory allocation to process data blocks securely and efficiently.
In the vulnerable versions of the code, certain paths within the AEGIS x86 optimized routines failed to verify whether the memory allocation request succeeded or failed.
If an attacker or low-privileged user triggers heavy cryptographic workloads under low-memory conditions, the missing error check can lead to a NULL pointer dereference.
When a NULL pointer is subsequently accessed or dereferenced without validation, the kernel triggers a panic, resulting in a denial of service (DoS).
Furthermore, improper error handling in low-level architecture-specific assembly or C wrapper functions can corrupt kernel state memory or cause unexpected execution faults.
The flaw highlights the critical importance of rigorous error propagation across all cryptographic subsystem drivers, especially those operating near hardware limits.
While local access and specific conditions are required to induce the memory failure state, the resulting kernel crash impacts system availability.
Mitigating this requires explicit return value verification for every `skcipher_walk` invocation to ensure safe fallback or graceful exit paths.
DailyCVE Form:
Platform: Linux Kernel
Version: Upstream 6.x
Vulnerability: Missing error check
Severity: Medium risk
date: September 2025
Prediction: Patched in upstream
What Undercode Say:
Analytics:
The architectural analysis of the x86 AEGIS crypto module reveals that neglecting return values from helper walkers introduces systemic instability under memory pressure. Code auditing demonstrates that kernel modules interacting directly with crypto APIs must rigorously handle allocation failures to prevent unhandled faults.
Exploit: (Educational Purposes!)
Bash commands and code snippet illustrating how the vulnerable cipher configuration can be invoked or tested locally:
Check loaded crypto modules related to aegis lsmod | grep aegis Trigger kernel crypto test suite for aegis modprobe tcrypt mode=400
C code logic showing the missing error check pattern in skcipher_walk:
int err;
struct skcipher_walk walk;
err = skcipher_walk_virt(&walk, req, false);
// Vulnerable code lacked proper error checking on err return value before loop execution
while (walk.nbytes) {
// perform AEGIS encryption/decryption operations
err = crypto_aegis_update(&walk);
skcipher_walk_done(&walk, err);
}
Protection: from this CVE
To protect against CVE-2025-39789, administrators and developers must update their Linux kernel packages to the versions incorporating the official patch by the kernel maintainers. The patch introduces robust error checking immediately following `skcipher_walk` calls, ensuring that allocation failures return `-ENOMEM` safely instead of proceeding with invalid pointers. Additionally, monitoring kernel ring buffers via `dmesg` helps detect early signs of subsystem instability.
Impact:
The impact of CVE-2025-39789 is localized primarily to system availability, categorized with a Medium severity score (CVSS base score around 5.5). An attacker capable of executing local code with low privileges can exhaust system resources or trigger memory exhaustion scenarios to induce a kernel panic, leading to denial of service. Confidentiality and integrity remain uncompromised since arbitrary code execution or privilege escalation is generally precluded by the nature of the fault.
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Sources:
Reported By: github.com
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