Remotely triggerable out-of-bounds heap write in dhclient
FreeBSD-SA-26:15.dhclient · CVE-2026-42512
Our decision for FreeSense
FreeBSD corrected this on 2026-04-29, before the FreeBSD source pin of every FreeSense version.
- Advisory: corrected 2026-04-29
- FreeSense 1.0 pin: e004ff15f87e (2026-08-03)
- FreeSense 1.1 pin: a52c50b4b7c2 (2026-10-04)
- FreeSense 1.2 pin: a52c50b4b7c2 (2026-10-04)
By FreeSense version
| Version | Status | FreeBSD pin |
|---|---|---|
| FreeSense 1.01.0.7 · frozen, no further fixes | FixedFreeBSD pin of 2026-08-03 | 2026-08-03e004ff15 |
| FreeSense 1.11.1.9 | FixedFreeBSD pin of 2026-10-04 | 2026-10-04a52c50b4 |
| FreeSense 1.21.2.0-DEVELOPMENT | FixedFreeBSD pin of 2026-10-04 | 2026-10-04a52c50b4 |
Workaround
No workaround is available. Systems not running dhclient(8) are not affected. The attacker needs to be on the same broadcast domain and respond to DHCP requests. A well-managed network will configure DHCP snooping on switches to prevent rogue DHCP servers from operating.
What FreeBSD says
As dhclient is building an environment to pass to dhclient-script, it may need to resize the array of string pointers. The code which expands the array incorrectly calculates its new size when requesting memory, resulting in a heap buffer overrun.
Impact
A specially crafted packet can cause dhclient to overrun its buffer of environment entries. This can result in a crash, but it may be possible to leverage this bug to achieve remote code execution.
Excerpt from the FreeBSD advisory. Read the original for the full text and the fix.