Listen to this Post
The CVE-2025-39924 vulnerability exists within the Enhanced Read-Only File System (erofs) component of the Linux kernel. It specifically concerns the handling of encoded extents, a feature used for data compression. The flaw is in the algorithm sanity checks performed when the kernel processes these encoded extents. The current validation logic does not correctly apply to newly implemented encoded extent types. This improper check fails to unify validation with the defined compression algorithm constants, namely `Z_EROFS_COMPRESSION_MAX` and Z_EROFS_COMPRESSION_RUNTIME_MAX. Furthermore, it does not ensure consistency with the `sbi->available_compr_algs` bitmask, which tracks the compression algorithms actually available on the system. Consequently, the kernel may accept and attempt to process an encoded extent using an invalid, unsupported, or incorrectly indexed compression algorithm. This mismatch during decompression operations can lead to out-of-bounds memory access, corruption of kernel data structures, or a failure to properly decode file data. The invalid state may trigger a kernel panic (oops), resulting in a denial of service (system crash). In worst-case scenarios, it could potentially be leveraged for more severe security compromises, though the primary risk is system instability. The fix corrects the algorithm selection logic to strictly use the authorized constants and cross-reference the available algorithms bitmap, thereby restoring proper validation.
Platform: Linux kernel
Version: Various
Vulnerability: Invalid algorithm check
Severity: Not specified
date: 10/01/2025
Prediction: Patch applied
What Undercode Say:
Analytics:
Check loaded erofs module
lsmod | grep erofs
Verify running kernel version
uname -r
Inspect kernel config for erofs
grep CONFIG_EROFS /boot/config-$(uname -r)
How Exploit:
Exploitation requires a crafted erofs filesystem image containing an encoded extent with an invalid or maliciously set algorithm identifier. When this image is mounted and the kernel attempts to decompress the extent, the flawed validation accepts the bad algorithm. This leads to improper memory access during decompression, potentially causing a kernel panic or corrupting critical memory.
Protection from this CVE
Apply the official kernel patch that corrects the algorithm validation. Update the Linux kernel to a version that includes the fix for CVE-2025-39924. Disable erofs use if not required.
Impact:
Kernel panic leading to denial of service. Potential memory corruption. File system data integrity issues.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
