CVE-2026-2940: Tiny Web Server Buffer Overflow Flaw

CVE-2026-2940 Overview

A memory corruption vulnerability has been identified in Zaher1307 tiny_web_server affecting the URL Handler component. This out-of-bounds write vulnerability exists within the tiny_web_server/tiny.c file and can be exploited remotely over the network without authentication. The exploit has been publicly disclosed, making this vulnerability particularly concerning for any deployments of this lightweight web server.

Critical Impact

Remote attackers can exploit this out-of-bounds write vulnerability to potentially corrupt memory, leading to denial of service or possible code execution on systems running the affected tiny_web_server software.

Affected Products

• Zaher1307 tiny_web_server up to commit 8d77b1044a0ca3a5297d8726ac8aa2cf944d481b
• All versions using continuous delivery/rolling releases (no fixed version numbers available)

Discovery Timeline

• 2026-02-22 - CVE-2026-2940 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2940

Vulnerability Analysis

This vulnerability is classified as an out-of-bounds write (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the URL Handler component, specifically within the tiny_web_server/tiny.c file. When processing maliciously crafted URL requests, the application fails to properly validate input boundaries, allowing attackers to write data beyond the allocated buffer space.

The network-based attack vector means exploitation can occur remotely without requiring any user interaction or prior authentication. The vulnerability can impact the confidentiality, integrity, and availability of the affected system through memory corruption.

Root Cause

The root cause stems from insufficient bounds checking in the URL parsing logic within tiny.c. When the URL Handler processes incoming HTTP requests, it does not adequately validate the length of URL components before writing them to memory buffers. This allows specially crafted requests to overflow allocated memory regions, resulting in out-of-bounds memory writes.

Attack Vector

The vulnerability can be exploited remotely via network requests to the tiny_web_server. An attacker can craft a malicious HTTP request with a specially formatted URL that triggers the out-of-bounds write condition. No authentication or user interaction is required, making this attack relatively straightforward to execute.

The vulnerability mechanism involves sending crafted URL data that exceeds expected buffer boundaries in the URL Handler component. When processed by the tiny.c file's parsing functions, this triggers memory corruption through out-of-bounds write operations. Technical details are available in the GitHub Issue Tracker Entry.

Detection Methods for CVE-2026-2940

Indicators of Compromise

• Abnormally long or malformed URL requests in web server access logs
• Unexpected process crashes or segmentation faults in tiny_web_server
• Memory corruption indicators or abnormal memory allocation patterns
• Unusual HTTP request patterns targeting the URL Handler component

Detection Strategies

• Deploy network-based intrusion detection rules to identify oversized or malformed URL requests
• Monitor tiny_web_server process stability for unexpected crashes or restarts
• Implement web application firewall rules to filter suspicious URL patterns
• Review system logs for segmentation faults or memory access violations

Monitoring Recommendations

• Enable verbose logging on tiny_web_server deployments to capture request details
• Configure alerting for process crashes or unexpected service restarts
• Monitor network traffic for anomalous HTTP request patterns targeting the server
• Implement memory monitoring to detect abnormal allocation behavior

How to Mitigate CVE-2026-2940

Immediate Actions Required

• Review deployments for any instances of Zaher1307 tiny_web_server
• Place affected servers behind a reverse proxy or web application firewall
• Restrict network access to trusted sources only if possible
• Monitor the GitHub repository for updates and patches
• Consider migrating to an alternative, actively maintained web server solution

Patch Information

No official patch is currently available. The project maintainer was notified through an issue report but has not responded. Since tiny_web_server uses continuous delivery with rolling releases, users should monitor the GitHub repository for any commits addressing this vulnerability after commit 8d77b1044a0ca3a5297d8726ac8aa2cf944d481b.

Additional technical details and vulnerability tracking information are available at VulDB #347312.

Workarounds

• Deploy a reverse proxy (nginx, HAProxy) in front of tiny_web_server to filter malicious requests
• Implement URL length limits and input validation at the network perimeter
• Restrict access to the web server using firewall rules to limit exposure
• Consider replacing tiny_web_server with a more actively maintained alternative until a patch is available

# Example: Restrict access to tiny_web_server using iptables
# Allow only trusted IP ranges to access the web server port
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP