Local Privilege Escalation (LPE) is a critical phase in most attacks. Once an attacker has a foothold within a compromised Linux container, an LPE exploit is how attackers achieve root-level access, break out of the container, and cause additional harm. With vast and complex capabilities such as the Linux kernel (spanning 25M+ lines of code), it’s not surprising that LPE vulnerabilities are discovered regularly by attackers and security researchers alike. Patching regularly and often helps, but there’s still a window of vulnerability in this process. So how can deploying BlueRock help cover this window? As an example, let’s take a closer look at a recent LPE vulnerability: CVE-2024-26581.

One of many LPEs: CVE-2024-26581

In January 2023, Linux kernel developers introduced a vulnerability that allows local authenticated attackers to escalate privileges by exploiting a use-after-free (UAF) condition in the nft_rbtree_gc_elem function of nftables – the modern successor to iptables – a core tool to manage network firewall rules in Linux. This exploit is particularly noteworthy because:

• Reliability: The exploit is highly reliable on a wide range of kernel versions without needing recompilation for specific versions, making it an attractive component for exploit chains.
  
• Techniques: It leverages trending memory manipulation techniques, similar to other sophisticated exploits, to achieve privilege escalation.
  
• Data-Only Attack: The exploit relies exclusively on user-space memory read/writes, avoiding changes to the execution flow of targeted programs, thereby evading many traditional security defenses.

The underlying vulnerability, while introduced in Jan 2023, wasn’t discovered, reported, and patched within the mainline Linux kernel until February 2024. It then took Linux distribution maintainers multiple subsequent months before the patch was available to upstream users. For most impacted organizations, the window of vulnerability was over 1.5+ years (because, let’s face it, no organization has a perfect and fast vulnerability management process).

Understanding Linux credential management

Before discussing BlueRock’s mitigation strategy, it’s essential to understand the Linux cred structure, as found in include/linux/cred.h. 

Altering these fields at runtime is a technique attackers use to silently escalate privileges, making it crucial to protect its integrity.  

This structure holds key security information for processes, including:

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• User and Group IDs (UID, GID): Determine the process's ownership and group memberships.
• Set User/Group IDs (SUID, SGID): Used for binaries requiring elevated privileges.
• Effective User/Group IDs (EUID, EGID): Control access permissions.
• Filesystem User/Group IDs (FSUID, FSGID): Used for file system operations.
• Capabilities: Fine-grained privilege controls (cap_inheritable, cap_permitted, cap_effective, cap_bset, cap_ambient).
• Supplementary Groups: Additional groups beyond the primary GID.
• Security Context: Includes Linux Security Module specific data.

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Here’s a simplified view of the cred structure.  

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struct cred {

    kuid_t uid;       // Real UID of the task

    kgid_t gid;       // Real GID of the task

    kuid_t suid;      // Saved UID of the task

    kgid_t sgid;      // Saved GID of the task

    kuid_t euid;      // Effective UID of the task

    kgid_t egid;      // Effective GID of the task

    kuid_t fsuid;     // UID for VFS operations

    kgid_t fsgid;     // GID for VFS operations

    kernel_cap_t cap_inheritable; // Inheritable capabilities

    kernel_cap_t cap_permitted;   // Permitted capabilities

    kernel_cap_t cap_effective;   // Effective capabilities

    kernel_cap_t cap_bset;        // Capability bounding set

    kernel_cap_t cap_ambient;     // Ambient capability set

    // ... other fields ...

};

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BlueRock Process Credential Protection: Mitigating LPEs in real-time

BlueRock's Process Credential Protection mechanism is designed to safeguard against unauthorized modifications to Linux process credentials—a critical aspect of many LPE vulnerabilities, including CVE-2024-26581. Here's how BlueRock mitigates this class of vulnerabilities in real-time:

• Real-time integrity protection‍
  • BlueRock’s unique real-time introspection of Linux allows BlueRock to assure the integrity of these credential structures, blocking unauthorized credential manipulation.‍
  • Example: If an attacker attempts to exploit CVE-2024-26581 to modify credentials and gain root access, BlueRock will see and block the unauthorized changes in real-time, preventing the escalation.

• High performance, no noise
  
  
  • Unlike the case with security agents that can impose significant performance penalties and generate many false positives, BlueRock’s real-time introspection and runtime integrity can be used with high performance application workloads, assuring that sanctioned use of the Linux credential structures can proceed with effectively zero performance penalty.
    
  • Further, any BlueRock alert that signals a violation of Linux credential integrity was attempted can be interpreted as a high-fidelity indication that a critical exploit-based behavior has been seen and stopped.
    
  • Example: During an attack that leverages the use-after-free condition, BlueRock’s behavioral analysis can detect the illegitimate privilege escalation and block the process before it gains elevated privileges.

• Resilient and reliable security controls‍
  • Conventional security agents which run inside the very workloads they attempt to protect can be easily smoke-screened or bypassed by an attacker.
  • BlueRock operates outside of the workloads it protects, leveraging CPU protection primitives to assure that its security controls cannot be altered or disabled, even by a root Linux user or by a compromised Linux process running with kernel privileges.‍
  • Example: If the attacker successfully manipulates nftables (or any other kernel-level tool) to corrupt memory and attempts to modify process credentials, BlueRock stops the process, thwarting further compromise.
    
    

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Think different: fewer fire drills

CVE-2024-26581 isn’t the first Linux-based LPE vulnerability – nor will it be the last. Defenders need to adopt proactive defense-in-depth strategies to effectively address security issues like these – instead of relying solely on reactive patch management.

By implementing real-time introspection and CVE-agnostic defense, without introducing noise or performance overhead, BlueRock provides a comprehensive mitigation strategy that protects against an entire class of attacks that target Linux credential structures to achieve unsanctioned privilege escalation. This mechanism gives teams more time to test, validate, and schedule security patches like these – similar to every other software patch – rather than treating each security patch as a never. ending. fire. drill.

As threats continue to evolve, it is imperative to adopt defensible, vulnerability-agnostic protections that can protect systems during the critical patch gap. BlueRock's unique approach ensures that systems remain secure, maintaining the integrity and security of process credentials against unauthorized modifications.