CVE-2026-49414: FreeBSD Privilege Escalation Vulnerability

CVE-2026-49414 Overview

CVE-2026-49414 is a local privilege-relevant vulnerability in the FreeBSD kernel ELF image activator. The activator clears per-process Address Space Layout Randomization (ASLR) preference flags for setuid binaries after computing the Position Independent Executable (PIE) base address instead of before. A user-requested ASLR disable remains in effect when the kernel selects the base address for a setuid PIE binary. An unprivileged local user can call procctl(2) before execve(2) to disable ASLR for a setuid PIE target. This weakens exploitation mitigations and materially assists any secondary memory corruption primitive present in that binary. The issue is tracked under CWE-179: Incorrect Behavior Order: Early Validation.

Critical Impact
An unprivileged local user can force a setuid PIE binary to load at deterministic addresses, removing ASLR as an exploitation barrier for co-resident memory corruption bugs.

Affected Products

FreeBSD 14.3 (base release through patch level p14)
FreeBSD 14.4 (base release through patch level p5)
FreeBSD 15.0 (base release through patch level p9)

Discovery Timeline

2026-06-27 - CVE-2026-49414 published to the National Vulnerability Database
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-49414

Vulnerability Analysis

The FreeBSD ELF image activator is responsible for mapping ELF binaries into memory during execve(2). For PIE binaries, the activator selects a randomized base address based on the current process ASLR policy. FreeBSD exposes procctl(2) with PROC_ASLR_CTL so a process can request that ASLR be disabled for itself and its descendants.

When the target of execve(2) is a setuid binary, the kernel must discard the caller-controlled ASLR preferences before selecting a load base. The affected code performs this reset, but does so after the PIE base address has already been computed. The ordering defect means the base address is derived while the attacker-controlled ASLR-disable flag is still honored, yielding a fixed, predictable load address for the privileged binary.

Root Cause

The defect is a sequencing error in the image activator. The kernel evaluates the per-process ASLR preference flag, uses it to compute the PIE base, and only afterward clears the flag for setuid execution. Security-relevant state must be sanitized before it is consumed, not after.

Attack Vector

Exploitation requires local access and the ability to execute a setuid PIE binary. The attacker calls procctl(2) with PROC_ASLR_CTL set to PROC_ASLR_FORCE_DISABLE, then invokes execve(2) on the target setuid PIE binary. The privileged process loads at a deterministic address. On its own the flaw does not grant code execution, but it removes ASLR as a mitigation for any other memory corruption bug reachable in that binary, converting probabilistic exploitation into deterministic exploitation.

No verified public proof-of-concept is available. See the FreeBSD Security Advisory FreeBSD-SA-26:32.elf for the vendor's technical description.

Detection Methods for CVE-2026-49414

Indicators of Compromise

Processes that invoke procctl(2) with PROC_ASLR_CTL set to disable ASLR immediately prior to execve(2) of a setuid binary.
Setuid PIE binaries observed executing with identical load base addresses across independent invocations by unprivileged users.
Core dumps or crash reports from setuid binaries showing deterministic mapping layouts inconsistent with kernel ASLR being active.

Detection Strategies

Audit execve events for setuid targets and correlate against preceding procctl calls in the same process lineage using kernel auditing (auditd) or DTrace.
Baseline the distribution of load addresses for common setuid PIE binaries and alert on repeated identical bases from non-root callers.
Hunt for local privilege escalation chains that combine an ASLR-disabling procctl call with execution of a setuid binary known to contain memory-safety issues.

Monitoring Recommendations

Enable FreeBSD audit classes covering process control and execution (pc, ex) and forward events to a centralized log platform for retention and correlation.
Track kernel and userland package versions across the fleet to identify hosts still running FreeBSD 14.3, 14.4, or 15.0 branches below the fixed patch level.
Alert on unusual sequences of procctl(PROC_ASLR_CTL, PROC_ASLR_FORCE_DISABLE) followed within milliseconds by execve of a setuid file, particularly from interactive shells.

How to Mitigate CVE-2026-49414

Immediate Actions Required

Apply the FreeBSD security patch referenced in FreeBSD-SA-26:32.elf to all affected 14.3, 14.4, and 15.0 systems.
Inventory setuid PIE binaries on affected hosts using find / -perm -4000 -type f and prioritize patching hosts that expose network-facing services relying on such binaries.
Restrict local shell access on multi-user FreeBSD systems until the kernel patch is deployed and hosts have been rebooted onto the fixed kernel.

Patch Information

FreeBSD has published a fix in the security advisory FreeBSD-SA-26:32.elf. Administrators should install the patched kernel using freebsd-update on supported release branches, or rebuild from the source tree at the fixed revision, and then reboot. Kernel-only patches require a reboot to take effect.

Workarounds

Remove the setuid bit from non-essential PIE binaries where the elevated privilege is not required, using chmod u-s.
Set the system-wide ASLR policy to enforced via sysctl kern.elf64.aslr.enable=1 and kern.elf64.aslr.pie_enable=1 and disallow per-process opt-out where operational requirements permit.
Constrain execution of setuid binaries to trusted users through jails, mac_bsdextended, or reduced group membership until the patch is applied.

bash

# Post-patch verification: confirm running kernel is at the fixed patch level
freebsd-version -k
uname -a

# Enumerate setuid PIE binaries for review
find / -xdev -perm -4000 -type f -exec file {} \; | grep -i 'pie executable'

# Enforce ASLR at the system level (values persist via /etc/sysctl.conf)
sysctl kern.elf64.aslr.enable=1
sysctl kern.elf64.aslr.pie_enable=1