CVE-2026-12235
MediumCVSS 6.3Exploitation Probability (EPSS)
Low risk1th percentile - higher than 1% of all known CVEs
Summary
The Linkable Loadable Extensions (llext) subsystem in Zephyr OS mishandles PLT/RELA relocation entries when linking relocatable ELF extensions on Xtensa. The lack of validation of the r_offset field allows an out-of-bounds write beyond the extension's text buffer, leading to memory corruption in supervisor context.
Risk Assessment
An attacker can exploit this vulnerability to perform an out-of-bounds write in supervisor mode, potentially causing loss of integrity and availability, and escaping the sandbox boundary for user-mode extensions.
Recommendation
Apply the fix that adds a bound check rejecting any RELA entry whose r_offset is greater than or equal to the target section size. Update the system to a patched version and avoid loading ELF extensions from untrusted sources.
Original NVD description (English source)
The Linkable Loadable Extensions (llext) subsystem mis-handles PLT/RELA relocation entries when linking a relocatable (partially-linked) ELF extension. In llext_link_plt() (subsys/llext/llext_link.c), the relocatable branch (tgt != NULL, the path used for Xtensa relocatable objects) computed the patch address as ext->mem[LLEXT_MEM_TEXT] - text.sh_offset + rela.r_offset + tgt->sh_offset and then performed the relocation write there without validating rela.r_offset. Its sibling shared/dynamic branch already rejected out-of-range offsets via llext_file_offset(). rela.r_offset is read directly from the ELF's RELA table, so a crafted entry with an offset larger than the target section makes the write land arbitrarily far outside the extension's text buffer. The result is an attacker-influenced out-of-bounds write (the location via r_offset, the written value being the resolved symbol address) performed in supervisor context at link time, before any extension code runs. The path is reached from llext_load() whenever an application loads an attacker-influenced ELF extension on Xtensa with writable storage; llext is documented to accept extensions of untrusted origin. Impact is supervisor-context memory corruption (integrity and availability loss, and a sandbox-boundary escape for user-mode extensions). Exploitation is gated by the Xtensa relocatable PLT path and writable storage, and turning the out-of-range write into a useful primitive is non-trivial. The fix adds a bound check rejecting any RELA entry whose r_offset >= tgt->sh_size, mirroring the existing validation in the shared branch.