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How the CVE works:
The vulnerability CVE-2025-39834 is a memory leak in the Linux kernel’s net/mlx5 subsystem, specifically within the Hardware Steering (HWS) component. In the function hws_action_get_shared_stc_nic, when an invalid stc_type parameter is provided, the function allocates kernel memory for a shared_stc structure. However, the error handling flow incorrectly jumps to a label called unlock_and_out without freeing this allocated memory. This bypasses the cleanup code that would normally deallocate the memory, causing a persistent leak. Each time this error condition is triggered—such as by sending malformed steering commands to the mlx5 driver—the kernel loses a portion of memory. Repeated exploitation can lead to gradual memory exhaustion, affecting system stability and performance. The leak occurs only when the invalid stc_type is encountered, typically through network interactions or driver commands. The fix modifies the error path to redirect to a label that includes proper memory deallocation, ensuring resource recovery. This vulnerability is relevant in environments using Mellanox mlx5 network cards with HWS features enabled, where such commands might be processed.
Platform: Linux kernel
Version: Multiple kernel versions
Vulnerability: Memory leak
Severity: Medium
Date: 2025-09-16
Prediction: Patch released 2025-09-16
What Undercode Say:
Analytics:
`uname -r` Check kernel version
`lsmod | grep mlx5` List mlx5 modules
`dmesg | grep -i memory` Monitor memory issues
`grep -r “hws_action_get_shared_stc_nic” /usr/src/linux` Find vulnerable code
how Exploit:
Send invalid stc_type commands repeatedly via network or driver interfaces to trigger memory leak, causing kernel memory exhaustion and potential denial of service.
Protection from this CVE:
Update Linux kernel to patched version, apply official kernel patches, disable mlx5 HWS if unused.
Impact:
Kernel memory exhaustion, system instability, denial of service.
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Sources:
Reported By: nvd.nist.gov
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