CVE-2026-24800: Furnace Zlib Buffer Overflow Vulnerability

CVE-2026-24800 Overview

CVE-2026-24800 is a critical Out-of-bounds Write and Classic Buffer Overflow vulnerability affecting the tildearrow furnace application, specifically within the extern/zlib modules. The vulnerability is associated with program files inflate.C, where improper handling of input data can lead to memory corruption through buffer overflows.

Critical Impact

This vulnerability enables attackers to write data beyond allocated buffer boundaries, potentially resulting in arbitrary code execution, system compromise, or denial of service conditions on affected systems.

Affected Products

• tildearrow furnace (extern/zlib modules)
• furnace versions with vulnerable inflate.C implementation

Discovery Timeline

• 2026-01-27 - CVE CVE-2026-24800 published to NVD
• 2026-01-27 - Last updated in NVD database

Technical Details for CVE-2026-24800

Vulnerability Analysis

This vulnerability stems from insufficient bounds checking when copying data into fixed-size buffers within the zlib decompression routines. The inflate.C file contains code that processes compressed data streams but fails to properly validate the size of incoming data before performing memory copy operations. When processing specially crafted compressed data, the application writes beyond the allocated buffer boundaries, corrupting adjacent memory regions.

The network-accessible nature of this vulnerability means attackers can trigger it remotely without requiring authentication or user interaction. The vulnerability allows attackers to achieve full compromise of confidentiality, integrity, and availability on the affected system, with potential for impacting neighboring systems as well.

Root Cause

The root cause is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a Classic Buffer Overflow. The inflate.C implementation does not adequately verify that the input data length fits within the destination buffer before performing the copy operation. This allows an attacker to supply input that exceeds the expected buffer size, causing memory corruption.

Attack Vector

The vulnerability is exploitable over the network with low attack complexity. An attacker can craft malicious compressed data that, when processed by the vulnerable zlib inflate routine, triggers the buffer overflow condition. The attack requires no privileges and no user interaction, making it highly exploitable in environments where furnace processes untrusted compressed data.

The exploitation flow involves:

1. Attacker prepares malformed compressed data designed to exceed buffer limits
2. Target application receives and processes the compressed data through furnace's zlib implementation
3. The inflate.C routine attempts to decompress without proper bounds checking
4. Memory corruption occurs as data is written beyond allocated boundaries
5. Attacker gains control over program execution or causes system crash

Detection Methods for CVE-2026-24800

Indicators of Compromise

• Unexpected crashes or segmentation faults in processes using furnace
• Memory corruption errors in application logs related to zlib operations
• Anomalous network traffic containing malformed compressed data payloads

Detection Strategies

• Deploy memory protection mechanisms such as ASLR, DEP, and stack canaries to detect exploitation attempts
• Monitor for abnormal process behavior including unexpected crashes in furnace or dependent applications
• Implement network-level inspection for malformed or oversized compressed data streams

Monitoring Recommendations

• Enable application-level logging for zlib decompression operations
• Configure crash dump collection to capture evidence of buffer overflow exploitation
• Monitor system resource usage for anomalies indicative of heap spraying or memory manipulation attacks

How to Mitigate CVE-2026-24800

Immediate Actions Required

• Review exposure of systems running furnace to untrusted network input
• Apply available patches or updates from the furnace project immediately
• Consider isolating affected systems until remediation is complete
• Implement network segmentation to limit potential blast radius

Patch Information

A fix has been submitted to the furnace project. Refer to GitHub Pull Request #2471 for patch details and updated code. Organizations should update to a patched version of furnace as soon as one is released incorporating this fix.

Workarounds

• Disable or restrict processing of untrusted compressed data until patch is applied
• Implement input validation at application boundaries to reject malformed compressed data
• Use compile-time hardening options such as -fstack-protector-strong and FORTIFY_SOURCE
• Consider using alternative, patched zlib implementations if available

# Example: Compile with hardening flags to reduce exploitation risk
gcc -fstack-protector-strong -D_FORTIFY_SOURCE=2 -o furnace furnace.c -lz