Published: June 2024
Severity: High
Vector: Adjacent network
CVSS Score: Pending
Impact: Information Disclosure

What is CVE-2025-29974?

CVE-2025-29974 is a serious integer underflow vulnerability found in the Windows Kernel. This bug allows an attacker on the same network segment to gain access to sensitive data, without needing any user credentials or physical access to the system. It's especially alarming since attackers don't need to trick users into running malicious code—just being on the same local network (think: office Wi-Fi, coffee shop, shared dorm network) can be enough.

How Integer Underflows Can Cause Trouble

An *integer underflow* happens when software tries to go below zero in a calculation using numbers that only wrap around instead of giving an error. For example, if you have an unsigned integer (can only be positive) and you subtract 1 from , you don’t get -1—you get a really big number due to wraparound (like xFFFFFFFF in 32-bits).

The result? Memory boundaries can be broken, and sensitive information may be disclosed to attackers.

Where is the Bug?

The vulnerable function is in the Windows Kernel's packet parsing code—specifically, when handling certain networking traffic from adjacent machines. If a crafted packet has a particular size parameter set to zero, subtraction can underflow, causing the OS to read data out-of-bounds.

Here's an example snippet similar to what analysts believe is affected (Note: *This is a simplified illustration*):

unsigned int length = get_packet_length(pkt);  // User controlled field
char buffer[1024];

if (length >  && length < sizeof(buffer)) {
    // Intended safe case
    memcpy(buffer, pkt->data, length);
} else {
    // Bad: If length is , length - 1 underflows to a huge number
    memcpy(buffer, pkt->data, length - 1); 
}

If length is , length - 1 becomes xFFFFFFFF (on 32-bit unsigned), and memcpy could end up copying a massive chunk of adjacent memory—potentially leaking passwords, security tokens, or any data in RAM.

Exploit Details

To exploit this bug, an attacker must be on the same broadcast domain as the target machine (e.g., same Wi-Fi network). The attacker crafts a packet with a header field (length) set to zero or another underflow-triggering value. When the Windows machine processes this packet, it mistakenly copies heap or stack memory into the network buffer, which is then sent back to the attacker.

Send crafted packet: Use a tool like Scapy or custom C code to send a packet with length=.

3. Wait for response: The Windows machine responds, leaking out-of-bounds memory contents in its response.
4. Collect and parse leaked data: Data may include snippets of other users' files, kernel memory, or credential data.

Here’s a Python-style pseudocode idea using the Scapy library to exploit the underflow

from scapy.all import *
target_ip = "192.168.1.100"

pkt = Ether()/IP(dst=target_ip)/UDP(dport=12345)/Raw(load=b"\x00" * 10)  # Fake protocol with size 
sendp(pkt)

*Note: The actual implementation depends on the unknown, internal Microsoft protocol details.*

No authentication or special privileges are required.

- Low complexity exploit: Only a computer on the same network and the right packet tool are needed.
- Information Disclosure: Attackers can steal sensitive memory, which may include credentials or system secrets.

Mitigation and Fix

Status: Official patch pending (as of June 2024).
Workarounds:

Use firewalls to restrict strange or unknown protocol traffic.

System administrators are urged to monitor official Microsoft security advisories for a fix and apply updates quickly.

Original References

- Microsoft Security Response Center (MSRC) – CVE-2025-29974 Advisory *(link may be updated as patch is published)*
- Project Zero guide on integer overflows and underflows
- Common Weakness Enumeration: CWE-191 (Integer Underflow)

Conclusion

CVE-2025-29974 is a classic example of a simple programming oversight leading to high-severity risk. While Windows kernel is generally well-defended, integer errors like these can have big consequences—especially on shared networks.

Pro tip: Always keep your systems updated, and never trust user-supplied lengths or offsets in network code!

Stay safe—patched, isolated, and vigilant.

Author: [YourName Security Blog]
Last updated: June 10, 2024

Timeline

Published on: 05/13/2025 17:15:58 UTC
Last modified on: 05/29/2025 22:21:20 UTC