CVE-2020-12403 Overview
A critical out-of-bounds read vulnerability was discovered in the CHACHA20-POLY1305 implementation within Mozilla Network Security Services (NSS). The flaw exists in how multi-part ChaCha20 encryption is handled, allowing attackers to trigger out-of-bounds memory reads that can lead to information disclosure and denial of service conditions.
Critical Impact
This vulnerability enables network-based attackers to read sensitive memory contents and crash affected applications without requiring authentication or user interaction, posing significant risks to confidentiality and system availability.
Affected Products
- Mozilla NSS versions prior to 3.55
- Systems and applications utilizing vulnerable NSS cryptographic libraries
- Linux distributions shipping affected NSS packages (Debian, Red Hat, etc.)
Discovery Timeline
- 2021-05-27 - CVE-2020-12403 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2020-12403
Vulnerability Analysis
The vulnerability resides in the ChaCha20-Poly1305 authenticated encryption implementation within Mozilla NSS. ChaCha20-Poly1305 is a widely-used authenticated encryption with associated data (AEAD) cipher that combines the ChaCha20 stream cipher with the Poly1305 message authentication code. When the multi-part ChaCha20 mode is utilized, the implementation fails to properly validate buffer boundaries, leading to out-of-bounds memory access.
The flaw specifically manifests when processing cryptographic operations in multi-part mode, where data is encrypted or decrypted in segments rather than as a single contiguous block. The improper handling of chunk boundaries allows memory reads beyond the intended buffer limits.
Root Cause
The root cause stems from insufficient bounds checking in the multi-part ChaCha20 encryption routines (CWE-125: Out-of-bounds Read). The implementation did not properly validate input lengths and buffer boundaries when processing data in segments, and the multi-part functionality was not operating correctly. Mozilla addressed this by explicitly disabling multi-part ChaCha20 support and implementing strict tag length enforcement to prevent exploitation.
Attack Vector
The vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can craft malicious encrypted payloads that trigger the out-of-bounds read condition when processed by the vulnerable NSS library. This can be achieved through:
- Sending specially crafted TLS handshake messages to servers using NSS
- Manipulating encrypted communications to trigger vulnerable code paths
- Exploiting applications that use NSS for cryptographic operations
The attack does not require prior access to the target system, making it particularly dangerous for internet-facing services utilizing vulnerable NSS versions.
Detection Methods for CVE-2020-12403
Indicators of Compromise
- Unexpected application crashes or segmentation faults in NSS-dependent services
- Abnormal memory access patterns in processes using NSS cryptographic functions
- Error logs indicating cryptographic operation failures with ChaCha20-Poly1305
- Unusual TLS connection behavior or malformed encrypted traffic patterns
Detection Strategies
- Monitor for NSS library crashes and abnormal termination events in system logs
- Implement network intrusion detection rules for malformed TLS traffic patterns
- Deploy application-level monitoring to detect unusual cryptographic operation failures
- Audit installed NSS library versions across infrastructure to identify vulnerable deployments
Monitoring Recommendations
- Configure centralized logging for all NSS-dependent applications and services
- Enable core dump analysis for processes experiencing unexpected termination
- Implement version tracking and alerting for cryptographic library dependencies
- Monitor for unusual network traffic patterns targeting TLS-enabled services
How to Mitigate CVE-2020-12403
Immediate Actions Required
- Upgrade Mozilla NSS to version 3.55 or later immediately
- Identify all applications and services dependent on NSS and prioritize patching
- Review TLS configurations to ensure proper cipher suite management
- Monitor systems for signs of exploitation attempts until patches are applied
Patch Information
Mozilla has addressed this vulnerability in NSS version 3.55. The fix explicitly disables multi-part ChaCha20 functionality (which was not working correctly) and implements strict tag length enforcement to prevent out-of-bounds read conditions. Organizations should consult the Mozilla NSS 3.55 Release Notes for detailed patch information.
Linux distributions have released corresponding security updates:
- Red Hat has tracked this issue in Red Hat Bug Report
- Debian LTS has published guidance in their Debian LTS Security Announcement
- NetApp has released advisories for affected products via their NetApp Security Advisory
Workarounds
- Disable ChaCha20-Poly1305 cipher suites in TLS configurations where feasible
- Implement network segmentation to limit exposure of vulnerable services
- Deploy web application firewalls with rules to detect malformed TLS traffic
- Consider temporary service isolation for critical applications until patching is complete
# Configuration example
# Check installed NSS version on Linux systems
rpm -qa | grep nss
# or for Debian-based systems
dpkg -l | grep libnss
# Verify NSS version meets minimum requirements
nss-config --version
# Should output 3.55 or higher
# Update NSS on Red Hat/CentOS systems
sudo yum update nss nss-util nss-sysinit
# Update NSS on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade libnss3
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
