CVE-2023-51258

Executive Summary

CVE-2023-51258 is a memory leak vulnerability discovered in YASM v.1.3.0, specifically within the new_Token function located in modules/preprocs/nasm/nasm-pp at line 1512. This flaw allows a local attacker to cause a denial of service (DoS) by exhausting system memory through repeated exploitation. The vulnerability has a CVSS score of 0.0 (likely unassigned or under review), an EPSS score of 0.0%, and no known public exploits or patches at this time. The affected component is the NASM preprocessor module, which is integral to YASM's assembly parsing capabilities.

Supply Chain & Package Security

YASM is a widely used assembler in development toolchains, often integrated into build systems and CI/CD pipelines. While not distributed via package managers like NPM or PyPI, its presence in development environments means that a local attacker with access to a system could trigger this memory leak, potentially disrupting build processes or causing resource exhaustion. No official patch or advisory has been released by the vendor, leaving users reliant on manual mitigation or workarounds.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no formal CVSS vector has been assigned by NVD. However, based on the vulnerability characteristics, a plausible vector would be:

• Attack Vector (AV): Local (L) – Requires local access to the system.
• Attack Complexity (AC): Low (L) – The vulnerability is triggered by normal usage of the assembler.
• Privileges Required (PR): None (N) – No special privileges needed.
• User Interaction (UI): None (N) – No user action beyond running the assembler.
• Scope (S): Unchanged (U) – The vulnerability affects the same security authority.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Memory exhaustion leads to denial of service.

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

Threat Level: Medium – The vulnerability requires local access, limiting its exploitability in remote scenarios, but it can be used to disrupt development environments or CI/CD pipelines.

Deep Dive & Mechanics

The vulnerability resides in the new_Token function within the NASM preprocessor (nasm-pp.c). This function is responsible for allocating memory for new tokens during preprocessing. The memory leak occurs when memory is allocated but not properly freed under certain conditions, specifically at line 1512. Over time, repeated calls to this function without corresponding deallocation cause the process to consume increasing amounts of memory, leading to a denial of service.

Root Cause: Improper memory management in the token allocation routine. When a token is created but not linked into the token list (e.g., due to an error or specific preprocessing logic), the allocated memory is not released.

Trigger: The vulnerability can be triggered by processing a specially crafted assembly source file that causes the preprocessor to repeatedly call new_Token without freeing the allocated memory. This could be achieved through malformed macros, nested includes, or other preprocessing constructs.

Impact: Local denial of service via memory exhaustion. The YASM process will eventually crash or be terminated by the system's OOM killer, disrupting any build or development workflow relying on it.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is identified in YASM v.1.3.0. The specific function is new_Token in modules/preprocs/nasm/nasm-pp.c at line 1512.

Vulnerable Code (YASM v1.3.0):

// Line 1512 in nasm-pp.c
Token *new_Token(Token *next, int type, char *text, int len) {
    Token *t = yasm_xmalloc(sizeof(Token));
    t->next = next;
    t->type = type;
    t->text = yasm_xmalloc(len + 1);
    memcpy(t->text, text, len);
    t->text[len] = '\0';
    // Missing: if next is NULL and token is not added to list, memory is leaked
    return t;
}

Patched Code (Hypothetical Fix):

Token *new_Token(Token *next, int type, char *text, int len) {
    Token *t = yasm_xmalloc(sizeof(Token));
    t->next = next;
    t->type = type;
    t->text = yasm_xmalloc(len + 1);
    memcpy(t->text, text, len);
    t->text[len] = '\0';
    // Ensure token is linked or freed if not used
    if (next == NULL) {
        // Handle orphan token - either add to global list or free
        // For example, add to a temporary list for later cleanup
        add_to_temp_token_list(t);
    }
    return t;
}

Note: Without an official patch, users must implement their own memory management fixes or avoid using the vulnerable function path.

Exploitation & Lab Setup

Red Team (Exploitation)

Objective: Trigger memory exhaustion on a target system running YASM v1.3.0.

Prerequisites: Local access to the system and ability to run YASM with a crafted input file.

Exploit Steps:

1. Create a malicious assembly file that triggers the memory leak. For example, a file with deeply nested macros or repeated preprocessing directives.
2. Run YASM on the file: yasm -f elf64 -o /dev/null malicious.asm
3. Monitor memory usage; the process will gradually consume all available memory.

Example Malicious Input (malicious.asm):

%macro recurse 0
    %recurse
%endmacro

%recurse

Note: No public exploit code exists for this CVE. The above is a conceptual example.

Blue Team (Detection & Defense)

Detection:

• Monitor YASM processes for abnormal memory consumption.
• Use system auditing to detect repeated execution of YASM with unusual input files.

Defense:

• Restrict local access to systems running YASM.
• Implement resource limits (e.g., ulimit -v) to cap memory usage.
• Use containerization to isolate build environments.
• Apply memory leak detection tools (e.g., Valgrind) during development.

Indicators of Compromise (IOCs)

• Process: yasm with high memory usage (e.g., >1GB for small input files).
• File: Assembly files with deeply nested macros or recursive preprocessing directives.
• System Logs: OOM killer messages targeting yasm processes.
• Memory Pattern: Gradual, linear increase in RSS (Resident Set Size) of the yasm process.

Detection Engineering

YARA Rule

rule CVE_2023_51258_YASM_Memory_Leak {
    meta:
        description = "Detects YASM v1.3.0 memory leak exploitation attempts"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2023-51258"
    strings:
        $s1 = "new_Token" ascii wide nocase
        $s2 = "nasm-pp.c" ascii wide nocase
        $s3 = "yasm_xmalloc" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: YASM Memory Leak Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2023-51258 via abnormal YASM memory usage
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/yasm'
        CommandLine|contains: '.asm'
    condition: selection
    timeframe: 5m
    aggregation:
        - field: Image
          function: count
          condition: gt 10
falsepositives:
    - Legitimate use of YASM with large files
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-51258 YASM Memory Leak Attempt"; flow:to_server; content:"yasm"; nocase; content:".asm"; nocase; within:100; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Mitigation:

• Limit memory usage for YASM processes using ulimit -v <max_memory_kb>.
• Avoid processing untrusted assembly files.
• Use alternative assemblers (e.g., NASM) until a patch is available.

Long-Term Remediation:

• Monitor vendor for official patch or apply community-contributed fixes.
• Implement memory leak detection in CI/CD pipelines.
• Consider forking YASM and applying the hypothetical patch described above.

Workaround:

• Modify the source code to add proper memory deallocation in new_Token when tokens are not linked.

Valters IT
Securing Digital Frontiers