Executive brief
aria2c is a popular command-line utility used for downloading files from the internet. A security flaw exists where the tool fails to properly verify the intended use of security certificates provided by servers. This could allow an attacker who has stolen a legitimate certificate meant for a different purpose (such as identifying a user) to impersonate a trusted website, potentially leading to the interception of downloaded data.
Technical details
aria2c is vulnerable to improper certificate validation (CWE-295) because it does not strictly enforce the Extended Key Usage (EKU) field during the TLS handshake. Specifically, the application accepts certificates that lack the 'TLS Web Server Authentication' (serverAuth) purpose, such as those only marked for 'TLS Web Client Authentication' (clientAuth). An attacker who has compromised a private key and a certificate issued for a non-server purpose could perform a man-in-the-middle (MitM) attack or host a malicious server that aria2c would trust as a legitimate endpoint. This vulnerability requires the attacker to possess a validly signed certificate from a trusted CA, albeit one with incorrect EKU attributes.
Affected products
- aria2 aria2c
Timeline
- 2026-05-13: disclosed: Vulnerability disclosed by Tenable Research.
- 2026-05-13: advisory: NVD published CVE-2026-8367.