The curl project has released a security update after researchers demonstrated that a vulnerability in HTTP/2 upload handling could allow a malicious server to corrupt client memory and potentially achieve code execution on an affected system. The issue, tracked as CVE-2026-92392, was addressed with the release of curl 8.23.0 on October 14, 2026. The vulnerability affects curl and libcurl versions 8.12.0 through 8.22.0, impacting both the command line tool and the widely used library that powers file transfers in many applications. curl classified the issue as High severity under its own four level rating system, marking its first High severity security issue since the SOCKS5 heap overflow vulnerability reported in October 2023.
The flaw is related to a use after free condition in the way libcurl manages HTTP/2 upload operations. For an attack to succeed, a user must upload a file of approximately 135KB to a server controlled by an attacker while using HTTP/2. The attacker controlled server must also have a valid certificate accepted by the client. Since libcurl automatically negotiates HTTP/2 for HTTPS connections when supported by the server, systems using builds with HTTP/2 functionality enabled may be exposed to this attack path. According to curl developers, successful exploitation requires detailed knowledge of the target environment, including the specific curl build, system architecture, memory layout and other technical conditions. The project noted that the most likely outcome of attempted exploitation would be a crash rather than successful code execution.
The vulnerability was publicly disclosed after the researcher who reported the issue released technical details, including a proof of concept demonstrating how the memory corruption could potentially be turned into code execution. According to curl developer Daniel Stenberg, the attack process involves a malicious server manipulating HTTP/2 communication by interrupting an upload, causing curl to retry the operation and creating a situation where previously released memory references can be accessed again. In the demonstrated scenario, the attacker uses carefully crafted data to influence memory contents and attempt to redirect program execution. However, the complexity of the exploit means successful exploitation requires precise timing and knowledge of the target system. curl stated that the risk of real world exploitation remains limited due to these requirements, which is why the vulnerability was rated High rather than Critical.
Users and organizations running affected versions are advised to upgrade to curl 8.23.0 or apply the available security fixes for supported branches. curl has also provided updates for older maintained versions, including fixes for specific release branches. As a temporary mitigation, users who cannot immediately update can disable HTTP/2 usage and force connections through HTTP/1.1 by using the appropriate configuration options. Applications using libcurl can also configure HTTP version settings to avoid negotiating HTTP/2 until updates are applied. The project confirmed that the security fix involved changes in how HTTP/2 connections manage references to transfer handles, reducing the risk of accessing released memory. The report was submitted through HackerOne on September 15 and was confirmed by the curl security team shortly afterward. The discovery was credited to Luna Tong of Anthropic through the company’s open source security scanning initiative, which uses AI supported analysis to identify potential vulnerabilities in open source projects. The curl team emphasized that while AI assisted security tools can help identify issues, human review and validation remain essential parts of vulnerability handling and software security processes.
Follow the SPIN IDG WhatsApp Channel for updates across the Smart Pakistan Insights Network covering all of Pakistan’s technology ecosystem.
