CVE-2021-31986: Axis OS Buffer Overflow Vulnerability

CVE-2021-31986 Overview

CVE-2021-31986 is a buffer overflow vulnerability affecting Axis network devices running various versions of Axis OS. The vulnerability exists in the SMTP notification functionality where user-controlled parameters are not correctly validated. This improper input validation can lead to a heap-based buffer overflow (CWE-122), resulting in system crashes and potential data leakage from affected devices.

Critical Impact

Successful exploitation of this vulnerability can cause denial of service through system crashes and enable unauthorized disclosure of sensitive information from Axis network cameras and devices.

Affected Products

• Axis OS (Active Track) - versions prior to security patch
• Axis OS 2016 (LTS)
• Axis OS 2018 (LTS)
• Axis OS 2020 (LTS)

Discovery Timeline

• October 5, 2021 - CVE-2021-31986 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-31986

Vulnerability Analysis

This vulnerability stems from improper handling of user-supplied input in the SMTP notification configuration of Axis OS devices. When users configure email notifications for events such as motion detection or system alerts, the parameters submitted through this interface are not properly validated before being processed by the underlying SMTP handling code.

The lack of boundary checking on these parameters allows an attacker to submit oversized or malformed data that exceeds the allocated buffer space. This results in a heap-based buffer overflow condition (CWE-122) combined with out-of-bounds write behavior (CWE-787). The exploitation requires network access to the device's management interface and some form of user interaction, such as clicking a malicious link or being social engineered to configure specific SMTP settings.

The impact of successful exploitation includes denial of service through application crashes and potential information disclosure. Memory corruption from the overflow may expose sensitive data stored in adjacent memory regions, which could include configuration details, credentials, or other operational data from the Axis device.

Root Cause

The root cause of CVE-2021-31986 is insufficient input validation in the SMTP notification parameter handling code. The affected code fails to properly verify the length and content of user-supplied strings before copying them into fixed-size buffers on the heap. This classic buffer overflow pattern occurs when the application trusts user input without implementing appropriate bounds checking or input sanitization routines.

Attack Vector

The attack vector for this vulnerability is network-based, requiring the attacker to have access to the device's web management interface. The attack complexity is considered high because successful exploitation depends on user interaction—an administrator or user must be tricked into configuring malicious SMTP parameters or clicking a crafted link that triggers the vulnerable code path.

The attacker would typically craft a malicious request containing oversized SMTP notification parameters. When processed by the vulnerable Axis OS device, these parameters overflow the designated buffer, potentially overwriting adjacent heap memory and causing unintended behavior ranging from crashes to memory disclosure.

Detection Methods for CVE-2021-31986

Indicators of Compromise

• Unexpected crashes or restarts of Axis network cameras and devices
• Anomalous network traffic to SMTP ports originating from Axis devices
• Error logs indicating memory corruption or segmentation faults in SMTP-related processes
• Unusual SMTP configuration changes in device settings

Detection Strategies

• Monitor Axis device logs for abnormal SMTP notification configuration attempts
• Implement network intrusion detection rules to identify oversized or malformed HTTP requests targeting Axis device management interfaces
• Deploy endpoint detection solutions capable of identifying buffer overflow exploitation attempts on IoT/embedded devices
• Audit SMTP notification configurations across all Axis devices for suspicious or unexpected entries

Monitoring Recommendations

• Enable comprehensive logging on all Axis network devices and forward logs to a centralized SIEM
• Configure alerts for repeated device crashes or unexpected reboots
• Monitor network traffic for connections to unauthorized SMTP servers from Axis devices
• Implement baseline monitoring for normal SMTP notification behavior to detect anomalies

How to Mitigate CVE-2021-31986

Immediate Actions Required

• Update all affected Axis devices to the latest firmware version that includes the security patch
• Restrict network access to device management interfaces using firewalls or VLANs
• Review and audit current SMTP notification configurations on all Axis devices
• Implement network segmentation to isolate surveillance and IoT devices from general network traffic

Patch Information

Axis Communications has released security updates to address this vulnerability. Detailed patch information and affected version numbers are available in the Axis Technology Note for CVE-2021-31986. Organizations should consult this advisory to determine the specific patched firmware versions for their device models and apply updates immediately.

Workarounds

• Disable SMTP notifications if not required for operational purposes until patches can be applied
• Implement strict access controls limiting who can modify SMTP notification settings
• Use a web application firewall (WAF) or reverse proxy to filter malicious requests to device management interfaces
• Enable additional authentication mechanisms for accessing device configuration pages

# Configuration example: Restrict management interface access via network segmentation
# Example iptables rules to limit access to Axis device management (port 80/443)
iptables -A INPUT -p tcp --dport 80 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP