CVE-2024-36031: Linux Kernel Privilege Escalation Flaw

CVE-2024-36031 Overview

CVE-2024-36031 is a vulnerability in the Linux kernel's key management subsystem where the expiry time of a key is unconditionally overwritten during instantiation. This flaw causes the key expiration to default to permanent (TIME64_MAX), which disrupts DNS resolution functionality by preventing user-space from setting proper expiration times for DNS keys. The vulnerability affects the kernel's key handling mechanism, specifically the key_set_expiry function behavior during key instantiation.

Critical Impact

This vulnerability can disable DNS updates by making keys permanent when they should expire, potentially leading to stale DNS records and network resolution failures that could be exploited for network-based attacks.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux (as noted in LTS announcements)
• Systems using kernel keyring for DNS resolution

Discovery Timeline

• 2024-05-30 - CVE CVE-2024-36031 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2024-36031

Vulnerability Analysis

The vulnerability resides in the Linux kernel's key management subsystem, specifically in how key expiration times are handled during the instantiation process. When a key is instantiated, the kernel unconditionally overwrites any expiration time that was previously set, defaulting the key to permanent status by setting it to TIME64_MAX. This behavior is particularly problematic for DNS key management, where user-space applications need to set specific expiration times to ensure DNS records are refreshed appropriately.

The flaw relates to CWE-324 (Use of a Key Past its Expiration Date), as the improper handling of key expiration effectively disables the expiration mechanism entirely. This can lead to situations where cryptographic keys or DNS resolver keys remain valid indefinitely, contrary to security best practices that mandate regular key rotation and expiration.

Root Cause

The root cause is the unconditional call to key_set_expiry during key instantiation, which overwrites any pre-existing expiration value set by user-space. The fix restores the conditional logic that only calls key_set_expiry when the pre-parser explicitly sets a specific expiry value, preserving user-space defined expiration times.

Attack Vector

The vulnerability can be exploited via network-based attack vectors. An attacker could potentially leverage the inability to properly expire DNS keys to maintain stale DNS records, facilitating DNS spoofing or cache poisoning attacks. Since DNS resolution relies on proper key expiration to refresh records, permanently valid keys could allow attackers to redirect traffic by preventing legitimate DNS updates.

The attack does not require privileges or user interaction, and can be exploited remotely through network-based DNS manipulation scenarios where the target system's DNS resolution becomes compromised due to stale, non-expiring keys.

Detection Methods for CVE-2024-36031

Indicators of Compromise

• DNS resolution failures or unexpected behavior on affected Linux systems
• Kernel keyring entries showing permanent expiration (TIME64_MAX) for DNS-related keys
• Log entries indicating key instantiation anomalies in /var/log/kern.log or dmesg output
• Stale DNS records persisting beyond expected TTL periods

Detection Strategies

• Monitor kernel logs for key subsystem messages related to DNS resolver keys
• Implement keyring monitoring to detect keys with unexpectedly long or permanent expiration times
• Deploy network monitoring to identify DNS resolution anomalies or stale record issues
• Use kernel auditing capabilities to track key instantiation events

Monitoring Recommendations

• Enable kernel audit logging for key management subsystem operations
• Configure alerts for DNS resolution failures that may indicate stale key issues
• Monitor system keyring status using keyctl utilities to identify affected keys
• Implement baseline comparisons for DNS key expiration values

How to Mitigate CVE-2024-36031

Immediate Actions Required

• Update the Linux kernel to a patched version containing the fix
• Review and restart any services dependent on DNS key management
• Clear and reinitialize kernel keyring entries for DNS resolver keys
• Monitor DNS resolution behavior after applying patches

Patch Information

The Linux kernel development team has released patches to address this vulnerability. Multiple kernel fix commits are available:

• Kernel Fix Commit 25777f3
• Kernel Fix Commit 939a08b
• Kernel Fix Commit 9da27fb
• Kernel Fix Commit ad2011e
• Kernel Fix Commit cc219cb
• Kernel Fix Commit e4519a0
• Kernel Fix Commit ed79b93

Debian users should refer to the Debian LTS Security Announcement for distribution-specific patch information.

Workarounds

• Manually manage DNS key expiration using keyctl utilities to set proper expiration times
• Implement application-level DNS caching with proper TTL enforcement as a temporary measure
• Consider using alternative DNS resolution mechanisms that don't rely on kernel keyring until patches are applied
• Schedule regular key refresh intervals through cron jobs or systemd timers

# Check current kernel keyring status for DNS keys
keyctl show @s

# View specific key expiration information
keyctl timeout <key_id> <timeout_seconds>

# Clear potentially affected DNS resolver keys (requires appropriate permissions)
keyctl clear @u