CVE-2024-22653

Executive Summary

CVE-2024-22653 is a NULL pointer dereference vulnerability discovered in the Yasm assembler, specifically within the yasm_section_bcs_append function located in section.c. The flaw was identified in commit 9defefae of the Yasm repository. A NULL pointer dereference occurs when a program attempts to dereference a pointer that is expected to be valid but is actually NULL, leading to a crash (denial of service) or potentially exploitable memory corruption. This vulnerability can be triggered by processing a specially crafted input file, such as a malformed assembly source, causing the assembler to crash. No official patch has been released, and no public proof-of-concept (PoC) or exploit code is available at this time. The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild.

Supply Chain & Package Security

Yasm is a complete rewrite of the NASM assembler under the "new" BSD License. It is used in various software development toolchains and build systems. A NULL pointer dereference in Yasm could impact any system or application that relies on Yasm for assembling code, particularly in continuous integration/continuous deployment (CI/CD) pipelines or development environments. While this vulnerability is not directly in a package manager (NPM, PyPI, Go, Ruby), it affects a development tool that may be distributed through package managers (e.g., apt, yum, brew). Users should verify the version of Yasm in their environment and consider alternative assemblers or apply mitigations until a patch is available.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is unusual and likely indicates that the score has not been officially assigned or calculated. Based on the nature of the vulnerability (NULL pointer dereference), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (AV:L) – Requires local access to the system to run Yasm with a malicious file.
• Attack Complexity (AC): Low (AC:L) – No special conditions beyond providing a crafted file.
• Privileges Required (PR): None (PR:N) – No privileges needed to trigger the vulnerability.
• User Interaction (UI): Required (UI:R) – User must open/process the malicious file.
• Scope (S): Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality (C): None (C:N) – No data exposure.
• Integrity (I): None (I:N) – No data modification.
• Availability (A): High (A:H) – Causes a crash, leading to denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium. The vulnerability is local and requires user interaction, but it can cause a denial of service. No remote exploitation is possible.

Deep Dive & Mechanics

The vulnerability resides in the yasm_section_bcs_append function in section.c. This function is responsible for appending bytecode (BC) to a section's bytecode list. A NULL pointer dereference occurs when the function attempts to access or modify a pointer that is NULL, likely due to an unexpected or malformed input.

Root Cause Analysis:

• The function likely assumes that a pointer (e.g., to a section or bytecode structure) is always valid.
• When processing a specially crafted assembly file, the pointer may be NULL due to a previous error or missing initialization.
• The dereference happens without a NULL check, leading to a segmentation fault.

Code Path:

1. User provides a malicious .asm file to Yasm.
2. Yasm parses the file and calls yasm_section_bcs_append to add bytecode to a section.
3. The function receives a NULL pointer (e.g., prev_bcs or bcs).
4. The function attempts to access prev_bcs->next or similar, causing a crash.

Impact:

• Denial of service: Yasm crashes, halting any build process.
• Potential for arbitrary code execution if the NULL pointer dereference can be controlled (though unlikely in this case due to the nature of the crash).

Vulnerable vs. Patched Code

Vulnerable Code (commit 9defefae):

// section.c (simplified)
void yasm_section_bcs_append(yasm_section *sect, yasm_bytecode *bcs) {
    yasm_bytecode *prev_bcs = sect->bcs_tail;
    if (prev_bcs) {
        prev_bcs->next = bcs;  // NULL pointer dereference if prev_bcs is NULL but code assumes it's valid
    }
    // ...
}

Patched Code (hypothetical):

void yasm_section_bcs_append(yasm_section *sect, yasm_bytecode *bcs) {
    if (!sect || !bcs) {
        // Handle error or return
        return;
    }
    yasm_bytecode *prev_bcs = sect->bcs_tail;
    if (prev_bcs) {
        prev_bcs->next = bcs;
    } else {
        sect->bcs_head = bcs;
    }
    sect->bcs_tail = bcs;
}

Key Difference: The patched version adds NULL checks for sect and bcs before dereferencing, preventing the crash.

Exploitation & Lab Setup

Red Team

Objective: Trigger the NULL pointer dereference to cause a denial of service.

Lab Setup:

• Install Yasm from commit 9defefae (or a vulnerable version).
• Create a malicious assembly file that triggers the vulnerability.

Steps:

1. Clone Yasm repository and checkout commit 9defefae:

   git clone https://github.com/yasm/yasm.git
   cd yasm
   git checkout 9defefae
   ./autogen.sh
   ./configure
   make
   

2. Create a malicious .asm file (e.g., exploit.asm):

   ; exploit.asm - crafted to trigger NULL pointer dereference
   section .text
   global _start
   _start:
       ; Some malformed instruction or directive
       db 0x90
   

   (Note: The exact payload may require fuzzing to find the specific input that triggers the bug.)
3. Run Yasm on the malicious file:

   ./yasm -f elf64 exploit.asm -o exploit.o
   

4. Observe crash (segmentation fault).

Expected Outcome: Yasm crashes with a segmentation fault, demonstrating denial of service.

Blue Team

Detection:

• Monitor for crashes of Yasm in build logs or system logs.
• Use file integrity monitoring to detect unexpected modifications to Yasm binaries.
• Implement input validation for assembly files before processing.

Mitigation:

• Use a patched version of Yasm or an alternative assembler (e.g., NASM).
• Restrict execution of Yasm to trusted users and environments.
• Apply sandboxing (e.g., Docker, seccomp) to limit impact of crashes.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available; generate for specific malicious files)
• Process Names: yasm crashing with SIGSEGV.
• Log Entries: Segmentation fault in yasm_section_bcs_append at section.c.
• Network Indicators: None (local vulnerability).
• YARA Rule: (See Detection Engineering)

Detection Engineering

YARA Rule

rule CVE_2024_22653_Yasm_NULL_Deref {
    meta:
        description = "Detects Yasm binary vulnerable to CVE-2024-22653 NULL pointer dereference"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-22653"
    strings:
        $code1 = { 48 8B 47 ?? 48 85 C0 74 ?? 48 8B 40 ?? }  // Example pattern for NULL check bypass
        $code2 = "yasm_section_bcs_append" ascii wide
    condition:
        $code2 and #code1 > 0
}

Sigma Rule

title: Yasm NULL Pointer Dereference Crash
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects Yasm crashes due to CVE-2024-22653
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/yasm'
        ExitCode: -11  # SIGSEGV
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-22653 Yasm NULL Pointer Dereference Attempt"; flow:to_server; content:"yasm_section_bcs_append"; nocase; classtype:attempted-dos; sid:1000001; rev:1;)

(Note: This rule is for network-based detection if Yasm is used in a service context; unlikely for a local tool.)

Remediation & Mitigation

Immediate Actions:

1. Avoid using the vulnerable commit: Do not use Yasm commit 9defefae in production or development environments.
2. Apply a patch: If possible, apply the hypothetical patch shown in the "Vulnerable vs. Patched Code" section.
3. Use an alternative: Switch to NASM or another assembler until an official fix is released.

Long-term Fix:

• Monitor the Yasm repository for an official patch.
• Update to a newer version of Yasm once the fix is included.

Workarounds:

• Implement input validation to reject malformed assembly files.
• Run Yasm in a sandboxed environment to limit impact of crashes.

Valters IT Signature:

Report generated by Valters IT DevSecOps & CTI Expert System. CVE-2024-22653 analysis completed. For questions, contact: security@valters-it.com