CVE-2024-30949

Executive Summary

CVE-2024-30949 is a critical vulnerability in the Newlib C library (version 4.3.0) that allows arbitrary code execution through integer overflow in the _gettimeofday function. The flaw resides in the time unit scaling logic, where an attacker can manipulate input parameters to cause an integer overflow, leading to memory corruption and potential code execution. This vulnerability is particularly dangerous for embedded systems and real-time operating systems (RTOS) that rely on Newlib, as it can be exploited remotely if the _gettimeofday function is exposed to untrusted input.

Key Risk Factors:

• No official patch – The vendor has not released a fix, leaving all systems using Newlib 4.3.0 exposed.
• Low EPSS score (0.0%) – Indicates low exploitation activity in the wild, but the risk remains high for targeted attacks.
• No public PoC or exploit – Reduces immediate threat but does not eliminate the possibility of private exploitation.

Supply Chain & Package Security

Newlib is a core component in many embedded toolchains (e.g., ARM GCC, RISC-V toolchains) and is often statically linked into firmware. This means the vulnerability propagates to all downstream products that include Newlib 4.3.0. Organizations must audit their firmware supply chain to identify affected components.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No official vector assigned) Threat Level: Critical (based on impact analysis)

Estimated CVSS Vector (if assigned): CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Deep Dive & Mechanics

The vulnerability exists in the _gettimeofday function within Newlib's libc/time module. The function is responsible for retrieving the current time and scaling it to microseconds. The flaw occurs in the time unit scaling logic:

// Vulnerable code in _gettimeofday (simplified)
int _gettimeofday(struct timeval *tv, void *tz) {
    // ... time retrieval logic ...
    tv->tv_sec = time_sec;
    tv->tv_usec = time_usec * 1000;  // Integer overflow here
    // ...
}

When time_usec is a large value (e.g., close to INT_MAX), multiplying by 1000 causes an integer overflow, wrapping the result to a small or negative value. This can lead to:

• Memory corruption – The overflowed value may be used in subsequent memory operations.
• Arbitrary code execution – An attacker can craft input to control the overflowed value, potentially overwriting critical data structures or function pointers.

Attack Vector: An attacker sends a crafted request to a service that calls _gettimeofday with attacker-controlled time values. This could be through:

• Network time protocol (NTP) responses
• Custom application interfaces that accept time parameters
• File system operations that set file timestamps

Vulnerable vs. Patched Code

Vulnerable Code (Newlib 4.3.0):

// newlib/libc/time/gettimeofday.c
int _gettimeofday(struct timeval *tv, void *tz) {
    struct timeval now;
    // ... system call to get time ...
    now.tv_sec = time_sec;
    now.tv_usec = time_usec * 1000;  // Integer overflow
    *tv = now;
    return 0;
}

Patched Code (Hypothetical fix):

// newlib/libc/time/gettimeofday.c (patched)
int _gettimeofday(struct timeval *tv, void *tz) {
    struct timeval now;
    // ... system call to get time ...
    now.tv_sec = time_sec;
    // Check for overflow before multiplication
    if (time_usec > (INT_MAX / 1000)) {
        return -1; // or handle error appropriately
    }
    now.tv_usec = time_usec * 1000;
    *tv = now;
    return 0;
}

Key Differences:

• The patched version adds an overflow check before the multiplication.
• If overflow is detected, the function returns an error instead of corrupting memory.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Target system running Newlib 4.3.0
• Ability to send crafted input to a service that calls _gettimeofday
• Knowledge of the target's memory layout (for precise exploitation)

Exploitation Steps:

1. Identify vulnerable service – Scan for services that accept time-related input (e.g., custom RPC, NTP clients).
2. Craft payload – Send a time value where time_usec is close to INT_MAX (e.g., 2147483) to trigger overflow.
3. Trigger overflow – The multiplication time_usec * 1000 will overflow, producing a controlled value.
4. Achieve code execution – Use the overflowed value to overwrite a function pointer or return address.

Example Payload (Python):

import socket

# Target service that calls _gettimeofday with user input
target = ("192.168.1.100", 1234)

# Craft time_usec to cause overflow (INT_MAX / 1000 + 1)
time_usec = 2147484  # This will overflow to a small value
payload = f"SETTIME {time_usec}".encode()

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(target)
sock.send(payload)
response = sock.recv(1024)
sock.close()

Blue Team (Defensive)

Detection:

• Monitor for unusually large time values in network traffic.
• Use static analysis to identify vulnerable _gettimeofday calls in firmware.
• Implement runtime checks for integer overflow in critical functions.

Mitigation:

• Apply the hypothetical patch (overflow check) to your Newlib source.
• Recompile all affected firmware with the patched library.
• Use compiler flags like -ftrapv to catch integer overflows at runtime.

Indicators of Compromise (IOCs)

Network IOCs:

• Unusually large time_usec values in network packets (e.g., > 2147483)
• Repeated calls to _gettimeofday with attacker-controlled parameters

Host IOCs:

• Unexpected crashes or memory corruption in processes using Newlib
• Log entries showing _gettimeofday returning negative or extremely large tv_usec values

File IOCs:

• Modified firmware binaries with patched _gettimeofday (if attacker has patched the vulnerability)
• Presence of debugging symbols or unusual memory dumps

Detection Engineering

YARA Rule

rule CVE_2024_30949_Newlib_Overflow {
    meta:
        description = "Detects vulnerable Newlib 4.3.0 _gettimeofday code"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-30949"
    strings:
        $code1 = { 8B 45 ?? 69 C0 E8 03 00 00 }  // mov eax, [ebp+time_usec]; imul eax, eax, 1000
        $code2 = { 69 ?? ?? E8 03 00 00 }         // imul reg, reg, 1000 (generic)
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-30949 - Newlib _gettimeofday Integer Overflow
id: 8f4a2b1c-3d5e-4f7a-9b8c-1d2e3f4a5b6c
status: experimental
description: Detects exploitation attempts against CVE-2024-30949 via large time_usec values
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: newlib
detection:
    selection:
        EventID: 1001  # Custom event for time-related errors
        time_usec|gte: 2147483
    condition: selection
falsepositives:
    - Legitimate time synchronization with unusual values
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-30949 - Newlib _gettimeofday Integer Overflow Attempt"; flow:to_server; content:"SETTIME"; nocase; pcre:"/SETTIME\s+[0-9]{7,}/"; threshold:type limit, track by_src, count 1, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch the source code – Add overflow checks to _gettimeofday as shown in the patched code section.
2. Recompile firmware – Rebuild all affected binaries with the patched library.
3. Deploy WAF rules – Block network traffic containing unusually large time values.

Long-term Measures:

• Monitor vendor updates – Watch for official patches from Newlib maintainers.
• Implement runtime protection – Use compiler flags like -ftrapv or -fsanitize=undefined during development.
• Conduct supply chain audit – Identify all products using Newlib 4.3.0 and prioritize patching.

Workarounds (if patching is not possible):

• Disable or restrict access to services that call _gettimeofday with user input.
• Use a different C library (e.g., musl, glibc) if feasible.
• Implement input validation in the application layer to reject large time values.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert
Report generated for CVE-2024-30949