CVE-2022-27781 in libcurl
Summary
by MITRE • 06/02/2022
libcurl provides the `CURLOPT_CERTINFO` option to allow applications torequest details to be returned about a server's certificate chain.Due to an erroneous function, a malicious server could make libcurl built withNSS get stuck in a never-ending busy-loop when trying to retrieve thatinformation.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability CVE-2022-27781 affects the libcurl library, a widely-used open-source tool for transferring data with URLs across various protocols including HTTP, HTTPS, and FTP. This security flaw specifically targets applications that utilize the CURLOPT_CERTINFO option, which enables developers to request detailed information about a server's certificate chain during SSL/TLS connections. The issue manifests when libcurl is compiled with the Network Security Services (NSS) library, a cryptographic toolkit developed by Mozilla. The vulnerability represents a denial-of-service condition that can severely impact the availability of applications relying on libcurl for secure communications.
The technical root cause of this vulnerability lies in an erroneous function within the NSS integration code of libcurl that handles certificate information retrieval. When a malicious server crafts a specially crafted certificate chain or response, it can trigger an infinite loop in the certificate processing logic. This occurs because the function responsible for parsing certificate information fails to properly validate or handle certain edge cases in the certificate data structure, causing the processing routine to repeatedly examine the same certificate elements without making forward progress. The busy-loop behavior consumes excessive CPU resources and prevents the application from continuing normal operations, effectively rendering the service unavailable to legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption, as it affects any application that depends on libcurl for secure communications and certificate validation. Systems using libcurl with NSS backend, including web browsers, email clients, network monitoring tools, and custom applications performing HTTPS requests, become vulnerable to this attack. The vulnerability is particularly concerning because it can be exploited remotely through malicious servers without requiring any authentication or privileged access. Attackers can simply set up a malicious HTTPS server that responds with crafted certificate data, causing any affected libcurl-based application to enter an infinite loop and consume all available CPU resources. This makes the vulnerability highly attractive for attackers seeking to disrupt services or perform resource exhaustion attacks against systems using vulnerable libcurl versions.
Organizations should immediately update their libcurl installations to versions that contain the patched implementation of the certificate information handling function. The fix typically involves adding proper boundary checks and validation logic to prevent the infinite loop condition when processing certificate data. Security teams should also implement network-level monitoring to detect unusual CPU consumption patterns that might indicate exploitation attempts. Additionally, applications using libcurl should consider implementing timeout mechanisms for certificate information retrieval operations to limit the impact of potential exploitation attempts. The vulnerability aligns with CWE-835, which covers infinite loops or iterations in software, and could be categorized under ATT&CK technique T1499.004 for network denial of service attacks. System administrators should prioritize patching systems with vulnerable libcurl installations, particularly those handling sensitive data or serving critical functions, to prevent exploitation and maintain service availability.