CVE-2026-35547: libnv Privilege Escalation Vulnerability

CVE-2026-35547 Overview

CVE-2026-35547 is a heap buffer overflow vulnerability affecting the libnv library in FreeBSD systems. When processing the header of an incoming message, libnv fails to properly validate the message size. This lack of validation allows a malicious program to write outside the bounds of a heap allocation, potentially triggering a crash, system panic, or enabling an unprivileged user to escalate their privileges.

Critical Impact
This vulnerability can lead to denial of service through system crashes or panics, and may be exploited by unprivileged local users to achieve privilege escalation on affected FreeBSD systems.

Affected Products

FreeBSD systems utilizing the libnv library
Applications and services that process messages via libnv
Systems where unprivileged users can send crafted messages to libnv-based services

Discovery Timeline

2026-04-30 - CVE-2026-35547 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-35547

Vulnerability Analysis

This vulnerability stems from a heap-based buffer overflow (CWE-122) in FreeBSD's libnv library, which is used for serializing and deserializing name/value pairs in interprocess communication. The core issue lies in the message header processing routine where the library accepts message size values from incoming data without adequate validation.

When a malicious actor supplies a crafted message with manipulated size parameters, the library allocates a heap buffer based on partial size information but then proceeds to write data that exceeds the allocated boundary. This out-of-bounds write condition corrupts adjacent heap memory, which can be leveraged in multiple ways depending on the attacker's goals and the system's memory layout.

The privilege escalation potential is particularly concerning because libnv is used in system-level communication contexts. An unprivileged local user who can interact with services using libnv may craft messages that corrupt heap metadata or overwrite function pointers, ultimately gaining elevated privileges on the system.

Root Cause

The root cause is improper input validation in the message header parsing logic of libnv. Specifically, the library trusts the message size field provided in the header without verifying that it matches the actual data being received or fits within safe allocation bounds. This allows attackers to specify a size that causes the library to allocate an insufficient buffer while subsequently writing more data than the buffer can accommodate.

Attack Vector

The attack requires local access to the system and the ability to send crafted messages to a service or process that utilizes libnv for message handling. An attacker would craft a malicious message with a manipulated size header that causes the library to:

Allocate a heap buffer based on the attacker-controlled size value
Process and write incoming data beyond the allocated buffer boundary
Corrupt adjacent heap memory structures

This heap corruption can then be exploited through various heap exploitation techniques to achieve arbitrary code execution with the privileges of the targeted process, potentially escalating from an unprivileged user to root or kernel-level access depending on the service being exploited.

The vulnerability manifests in the message header parsing and buffer allocation routines within libnv. Technical details and the specific affected code paths are documented in the FreeBSD Security Advisory.

Detection Methods for CVE-2026-35547

Indicators of Compromise

Unexpected system crashes or kernel panics related to heap corruption
Anomalous process behavior or privilege changes for services using libnv
Memory corruption errors in system logs referencing libnv or related components
Unusual interprocess communication patterns with malformed message sizes

Detection Strategies

Monitor system logs for kernel panics or heap corruption messages involving libnv
Implement heap canary and memory sanitizer tools in development environments to detect overflow attempts
Deploy runtime application self-protection (RASP) solutions that can detect heap overflow exploitation
Use SentinelOne Singularity to monitor for privilege escalation attempts and anomalous process behavior

Monitoring Recommendations

Enable verbose logging for services that utilize libnv for message processing
Configure alerting on unexpected privilege changes or process crashes
Monitor for signs of heap spray or heap grooming attacks that may precede exploitation
Implement process behavior monitoring to detect post-exploitation activity

How to Mitigate CVE-2026-35547

Immediate Actions Required

Apply the security patch provided by FreeBSD as documented in FreeBSD-SA-26:17
Identify all systems running affected versions of FreeBSD with libnv
Restrict local user access on critical systems until patches can be applied
Monitor affected systems for signs of exploitation attempts

Patch Information

FreeBSD has released a security advisory addressing this vulnerability. System administrators should apply the patches detailed in FreeBSD Security Advisory FreeBSD-SA-26:17.libnv. The patch adds proper validation of message size fields in the header processing routine to prevent out-of-bounds writes.

Workarounds

Limit local user access to only trusted users on systems where patching is delayed
Implement additional access controls on services that utilize libnv
Consider network segmentation to limit exposure of affected services
Deploy compensating controls through endpoint protection solutions like SentinelOne

bash

# Check FreeBSD version and apply security updates
freebsd-version
freebsd-update fetch
freebsd-update install
# Restart affected services after patching
service -R