CVE-2026-12200: TinyWeb Server Stack Buffer Overflow in Authorization Header

Technical summary

CVE-2026-12200 is a stack-based buffer overflow (CWE-121) introduced via improper input validation (CWE-119) in the Header Handler component of Ritlabs TinyWeb Server affecting version 1.94 and prior. The vulnerability resides in the processing of the Authorization HTTP header field. An attacker crafting an oversized or malformed Authorization header can trigger memory corruption, bypassing bounds checking in the libeay32.dll.html library component on Win32 systems. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L) reflects remote exploitability with low attack complexity and no privilege or user interaction requirements.

Business impact

Organizations running TinyWeb Server 1.94 for web hosting, file serving, or embedded applications face immediate risk of service disruption, data exfiltration, and potential code execution under the context of the web server process. The public disclosure and vendor non-responsiveness mean exploit tooling may become readily available, lowering the barrier for opportunistic attacks. Affected services may be rapidly compromised without evidence of legitimate authentication, increasing incident investigation complexity.

Affected systems

Ritlabs TinyWeb Server version 1.94 and all prior versions on Win32 (32-bit Windows) platforms are affected. No patched version has been indicated by the vendor. Organizations should conduct an asset inventory to identify TinyWeb Server instances in development, production, test, and legacy environments, including embedded or discontinued deployments that may still be accessible.

Exploitability

This vulnerability has a CVSS score of 7.3 (HIGH) and is classified as non-networked exploitation with minimal complexity. Public exploit disclosure has occurred, and the vendor has not responded to early disclosure attempts, meaning defensive patches are unlikely to emerge promptly. The attack surface is broad: any system accepting HTTP connections is at risk if TinyWeb Server is running. Exploitation requires only network access and knowledge of the vulnerable header parsing behavior—no specialized tools or elevated privileges are necessary.

Remediation

Immediate mitigation includes discontinuing or isolating affected TinyWeb Server instances from untrusted networks. Verify against the vendor advisory and monitor Ritlabs channels for a security update; however, given the non-responsive posture, consider alternative web server software (Apache, Nginx, IIS) for mission-critical deployments. If TinyWeb Server cannot be immediately replaced, implement network-level filtering to block or sanitize HTTP Authorization headers at a perimeter firewall or web application firewall, though this is not a substitute for patching.

Patch guidance

As of the published date, no vendor patch has been released or announced. Organizations should monitor the official Ritlabs TinyWeb Server website and security advisories for updates. If a patch becomes available, test it in a non-production environment before deployment. Given vendor non-responsiveness, evaluate the long-term viability of TinyWeb Server for your infrastructure and plan a migration timeline to a maintained alternative.

Detection guidance

Monitor web server logs for HTTP requests containing unusually long or malformed Authorization headers, particularly those exceeding expected RFC 7235 lengths (typically under 500 bytes). Implement network intrusion detection signatures targeting oversized header payloads to TinyWeb Server instances. Enable Windows event logging and memory protection features (DEP/ASLR) where possible to detect and log buffer overflow exploitation attempts. Correlate web server process crashes or unexpected restarts with preceding HTTP requests.

Why prioritize this

This vulnerability merits immediate attention due to its combination of remote exploitability, high CVSS score (7.3), public exploit availability, and vendor non-responsiveness. It requires no authentication or user interaction, giving attackers a wide attack surface. Organizations with exposed TinyWeb Server instances face imminent compromise risk and should treat this as a critical remediation priority.

Risk score, explained

The CVSS 3.1 score of 7.3 reflects a HIGH-severity vulnerability with remote network exploitability (AV:N), low attack complexity (AC:L), and no authentication or user interaction requirement (PR:N/UI:N). The attack impacts confidentiality, integrity, and availability at the individual scope level, aligning with the immediate threat posed by stack-based buffer overflow. Absent a vendor security update and with public disclosure, the practical risk to organizations running affected versions is elevated beyond the baseline score.

Frequently asked questions