Listen to this Post
CVE-2025-39836 is a vulnerability in the Linux kernel’s EFI System Trusted Management Module (STMM) driver. The issue arises from the setup_mm_hdr() function, which allocates a communication buffer for interacting with the Trusted Execution Environment (TEE). This function incorrectly uses kmalloc() to allocate memory. kmalloc() utilizes the kernel’s slab allocator and does not guarantee that the allocated memory consists of physically contiguous pages. However, this buffer is later passed to tee_shm_register_kernel_buf(), a function that registers kernel buffers with the TEE and explicitly requires buffers to be composed of contiguous physical pages. When tee_shm_register_kernel_buf() operates on a non-contiguous buffer allocated by kmalloc(), it can lead to memory corruptions, kernel bugs (such as BUG_ON() triggers), or system crashes. This mismatch was inherently problematic but became more severe after changes in the slab allocator from commit 9aec2fb0fd5e (“slab: allocate frozen pages”). The vulnerability could be exploited to cause denial of service by crashing the kernel or, potentially, allow for privilege escalation if kernel memory corruption is leveraged further. The fix involves replacing kmalloc() with alloc_pages_exact() in setup_mm_hdr(), ensuring that contiguous pages are allocated as required.
Platform: Linux Kernel
Version: Various versions
Vulnerability: Buffer allocation error
Severity: Not specified
Date: 09/16/2025
Prediction: Patch after 2025-09-16
What Undercode Say:
Analytics:
Bash command to check kernel version: `uname -r`
Bash command to search for fix: `git log –grep=”CVE-2025-39836″`
Vulnerable code snippet: `buffer = kmalloc(size, GFP_KERNEL);`
Fixed code snippet: `buffer = alloc_pages_exact(size, GFP_KERNEL);`
how Exploit:
Trigger setup_mm_hdr() repeatedly to cause memory corruption, leading to kernel panic or possible code execution.
Protection from this CVE
Apply kernel patches updating to fixed versions.
Impact
Denial of service, system crashes, potential privilege escalation.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
