# CVE-2026-12235: Out-of-bounds write in Xtensa llext PLT relocation from malformed ELF (CWE-787)

Status: published. Published: 2026-08-12. Updated: 2026-11-04.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/zephyrproject-rtos/zephyr/commit/106540afbd22087ad40b90f53fb22657754a719e

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 3.7.0; < 4.3.2 (affected, semver); ≥ 4.4.0; < 4.4.2 (affected, semver). Source: CNA: zephyr

## Severity and prioritization

- CVSS 3.1: 6.3 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H; source: CNA: zephyr

- CVSS 3.1: 6.3 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H; source: NVD: vulnerabilities@zephyrproject.org

- CISA KEV: No listing in collected sources

- EPSS: 0.14% as of 2026-11-03; percentile 3.13%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-787

## Exploit evidence

- exploit: https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xv9q-6mrf-8j49 (ADP: CISA-ADP)

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/106540afbd22087ad40b90f53fb22657754a719e (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xv9q-6mrf-8j49 (CNA: zephyr)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xv9q-6mrf-8j49 (ADP: CISA-ADP; exploit)

- https://github.com/zephyrproject-rtos/zephyr/commit/106540afbd22087ad40b90f53fb22657754a719e (vulnerabilities@zephyrproject.org)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xv9q-6mrf-8j49 (vulnerabilities@zephyrproject.org)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xv9q-6mrf-8j49 (134c704f-9b21-4f2e-91b3-4a467353bcc0)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-12235; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12235; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-12235; retrieved 2026-11-04; source updated Not reported

Revision: 6af92e1720bc2a6a1ea18efd9a20bd8200c00fcc5b1c6fe7d7cdf71e5e7e9a0a

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