CVE-2022-4450: OpenSSL Double Free DoS Vulnerability

CVE-2022-4450 Overview

CVE-2022-4450 is a double free vulnerability in OpenSSL's PEM_read_bio_ex() function that can be exploited to cause a denial of service. The function reads a PEM file from a BIO and parses and decodes the "name" (e.g., "CERTIFICATE"), header data, and payload data. When the function succeeds, it populates the name_out, header, and data arguments with pointers to buffers containing the decoded data. The caller is responsible for freeing those buffers.

The vulnerability occurs when a specially crafted PEM file results in 0 bytes of payload data. In this case, PEM_read_bio_ex() returns a failure code but populates the header argument with a pointer to a buffer that has already been freed. If the caller also attempts to free this buffer, a double free condition occurs, most likely leading to a crash.

Critical Impact

An attacker who can supply malicious PEM files for parsing can achieve a denial of service attack by triggering the double free condition in OpenSSL's PEM parsing functions.

Affected Products

• OpenSSL (multiple versions)
• Stormshield Network Security
• Any application using affected OpenSSL PEM parsing functions

Discovery Timeline

• 2023-02-07 - OpenSSL releases security advisory
• 2023-02-08 - CVE-2022-4450 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2022-4450

Vulnerability Analysis

This vulnerability is classified as CWE-415 (Double Free). The issue stems from improper memory management in the PEM_read_bio_ex() function when handling edge cases involving zero-byte payloads.

When parsing a PEM file, the function allocates buffers for the name, header, and data components. Under normal circumstances, if parsing succeeds, the caller takes ownership of these buffers and is responsible for freeing them. However, when a malformed PEM file with zero payload bytes is processed, the function enters an error path but leaves a stale pointer in the header argument that points to already-freed memory.

The vulnerability affects multiple OpenSSL functions that wrap or call PEM_read_bio_ex(), including:

• PEM_read_bio()
• PEM_read()
• PEM_X509_INFO_read_bio_ex()
• SSL_CTX_use_serverinfo_file()
• The openssl asn1parse command-line application

Some internal OpenSSL uses are not vulnerable because they do not free the header argument when PEM_read_bio_ex() returns a failure code. These protected locations include the PEM_read_bio_TYPE() functions and decoders introduced in OpenSSL 3.0.

Root Cause

The root cause is improper cleanup of internal state when PEM_read_bio_ex() encounters an error condition with zero-byte payload data. The function frees the header buffer internally but still returns the pointer to the caller, creating a use-after-free scenario that becomes a double free when the caller follows standard cleanup procedures.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker must have the ability to supply malicious PEM files to an application that uses the vulnerable OpenSSL functions for parsing. This could occur in scenarios such as:

• Certificate validation processes
• TLS server configuration loading
• Any application accepting PEM-formatted data from untrusted sources

The attacker constructs a malformed PEM file that produces zero bytes of payload data after decoding. When this file is processed by an application using the vulnerable functions, the double free is triggered, causing the application to crash.

Detection Methods for CVE-2022-4450

Indicators of Compromise

• Unexpected application crashes in processes handling PEM file parsing
• Core dumps showing double free or memory corruption in OpenSSL-related code paths
• Error logs indicating PEM parsing failures followed by segmentation faults
• Abnormal termination of TLS-enabled services after processing certificate files

Detection Strategies

• Monitor application logs for OpenSSL error messages related to PEM parsing failures
• Implement memory sanitizers (ASan, MSan) in development environments to detect double free conditions
• Deploy runtime protection mechanisms that can detect heap corruption
• Use SentinelOne's behavioral AI to detect abnormal process termination patterns

Monitoring Recommendations

• Set up alerts for repeated crashes of services that handle PEM files
• Monitor for unusual patterns of malformed certificate submissions
• Track OpenSSL-related error messages across your infrastructure
• Implement file integrity monitoring on configuration files containing PEM data

How to Mitigate CVE-2022-4450

Immediate Actions Required

• Update OpenSSL to a patched version immediately
• Review applications that accept PEM files from untrusted sources
• Implement input validation to reject malformed PEM files before processing
• Consider deploying Web Application Firewalls (WAF) to filter malicious certificate data

Patch Information

OpenSSL has released patches to address this vulnerability. The fixes are available in the following commits:

• OpenSSL Commit 63bcf189
• OpenSSL Commit bbcf509b

For detailed information about affected versions and remediation steps, refer to the OpenSSL Security Advisory.

Additional vendor-specific advisories:

• Gentoo GLSA 202402-08
• SonicWall Vulnerability Advisory SNWLID-2023-0003

Workarounds

• If immediate patching is not possible, restrict PEM file parsing to trusted sources only
• Implement strict input validation on PEM files before processing
• Isolate services that handle untrusted PEM data in sandboxed environments
• Consider disabling functionality that accepts PEM files from external sources until patches can be applied

# Verify OpenSSL version to confirm patched status
openssl version -a

# Check linked OpenSSL version in applications
ldd /path/to/application | grep ssl

# Update OpenSSL on Debian/Ubuntu systems
apt update && apt upgrade openssl libssl3

# Update OpenSSL on RHEL/CentOS systems
yum update openssl