CVE-2022-42898: MIT Kerberos 5 RCE Vulnerability

CVE-2022-42898 Overview

CVE-2022-42898 is an integer overflow vulnerability in the Privilege Attribute Certificate (PAC) parsing functionality of MIT Kerberos 5 (krb5) before version 1.19.4 and versions 1.20.x before 1.20.1. The flaw exists in krb5_pac_parse within lib/krb5/krb/pac.c and can lead to remote code execution on 32-bit platforms through a resultant heap-based buffer overflow. On other platforms, the vulnerability causes a denial of service condition. Heimdal versions before 7.7.1 contain a similar vulnerability.

Critical Impact

Authenticated attackers can exploit this integer overflow to achieve remote code execution on vulnerable KDC, kadmind, or GSS/Kerberos application servers running on 32-bit platforms. The vulnerability affects critical authentication infrastructure components.

Affected Products

• MIT Kerberos 5 versions before 1.19.4
• MIT Kerberos 5 versions 1.20.x before 1.20.1
• Heimdal versions before 7.7.1
• Samba (multiple affected versions)

Discovery Timeline

• December 25, 2022 - CVE-2022-42898 published to NVD
• April 14, 2025 - Last updated in NVD database

Technical Details for CVE-2022-42898

Vulnerability Analysis

The vulnerability exists in the PAC parsing code within MIT Kerberos 5, specifically in the krb5_pac_parse function located in lib/krb5/krb/pac.c. The PAC (Privilege Attribute Certificate) is a Microsoft extension to Kerberos that carries authorization data including user group memberships and other security-relevant information.

The integer overflow occurs when processing the number of buffers specified in a maliciously crafted PAC structure. When the buffer count is multiplied to calculate memory allocation sizes, the arithmetic operation can overflow on 32-bit platforms, resulting in a smaller-than-expected memory allocation. Subsequent operations then write beyond the allocated buffer boundaries, causing a heap-based buffer overflow.

On 64-bit platforms, while the integer overflow may not lead directly to code execution, the malformed PAC data can still trigger denial of service conditions by causing unexpected behavior in the authentication process.

Root Cause

The root cause is the absence of proper bounds checking on the number of PAC buffers before performing arithmetic operations that calculate memory allocation sizes. The integer overflow vulnerability (CWE-190) occurs because the code did not validate that the buffer count would not cause arithmetic overflow when multiplied by the size of buffer metadata structures. This allows an attacker to supply a crafted PAC with an extremely large buffer count that, when multiplied, wraps around to a small value, leading to insufficient memory allocation followed by heap corruption during parsing.

Attack Vector

The attack is network-based and requires low-privilege authentication to the Kerberos system. An attacker who has obtained valid Kerberos credentials (even with minimal privileges) can forge or manipulate PAC data within Kerberos tickets. When these malicious tickets are processed by vulnerable KDC servers, kadmind daemons, or application servers using GSS-API with Kerberos, the integer overflow is triggered during PAC parsing.

On 32-bit systems, successful exploitation can lead to arbitrary code execution with the privileges of the Kerberos service (typically root or SYSTEM). On 64-bit systems, the attack results in service crashes causing denial of service to authentication infrastructure.

// Security patch adding MAX_BUFFERS limit - Source: GitHub krb5 Commit ea92d2f
#include "int-proto.h"
#include "authdata.h"

+#define MAX_BUFFERS 4096

/* draft-brezak-win2k-krb-authz-00 */

/*

Source: GitHub krb5 Commit ea92d2f

The patch introduces a MAX_BUFFERS constant of 4096 to prevent the integer overflow by limiting the number of buffers that can be specified in a PAC structure.

Detection Methods for CVE-2022-42898

Indicators of Compromise

• Abnormal crashes or restarts of KDC, kadmind, or Kerberos-enabled application services
• Unusual authentication failures or service unavailability in Kerberos infrastructure
• Evidence of heap corruption or memory access violations in Kerberos service logs
• Presence of malformed Kerberos tickets with unusually large PAC buffer counts

Detection Strategies

• Monitor Kerberos service processes for unexpected crashes or memory corruption errors
• Implement network intrusion detection rules to identify Kerberos traffic with anomalous PAC structures
• Deploy endpoint detection to identify exploitation attempts against authentication services
• Review system logs for segmentation faults or heap overflow indicators in KDC and kadmind processes

Monitoring Recommendations

• Enable detailed logging for Kerberos authentication services to capture PAC parsing errors
• Configure alerting on KDC and kadmind service restarts or unexpected terminations
• Monitor memory usage patterns for Kerberos services to detect anomalous allocation behavior
• Implement file integrity monitoring on Kerberos binaries and configuration files

How to Mitigate CVE-2022-42898

Immediate Actions Required

• Upgrade MIT Kerberos 5 to version 1.19.4 or later (for 1.19.x branch) or 1.20.1 or later (for 1.20.x branch)
• Update Heimdal to version 7.7.1 or later
• Apply Samba security updates as specified in the Samba CVE-2022-42898 Advisory
• Prioritize patching of 32-bit systems due to higher exploitation impact

Patch Information

Security patches are available from the respective vendors:

• MIT Kerberos: Patched in versions 1.19.4 and 1.20.1. The fix adds a MAX_BUFFERS limit of 4096 to prevent integer overflow during PAC parsing. Details available at the MIT Kerberos Advisories page and MIT krb5 Version 1.20 README.
• Heimdal: Patched in version 7.7.1. See the GitHub Security Advisory GHSA-64mq-fvfj-5x3c for details.
• Samba: Security updates available. Refer to Samba Bugzilla Report #15203 for tracking.

Workarounds

• Isolate Kerberos infrastructure on dedicated network segments with restricted access
• Implement strict network access controls to limit which systems can communicate with KDC and kadmind services
• Consider migrating vulnerable 32-bit Kerberos deployments to 64-bit platforms to reduce exploitation severity
• Monitor for and block suspicious Kerberos ticket requests at network boundaries where feasible

# Verify installed krb5 version on Linux systems
krb5-config --version

# Check Samba version for vulnerability assessment
samba --version

# Review Kerberos service status
systemctl status krb5kdc kadmin