# CVE-2026-8367: aria2c accepts a server certificate with incorrect Extended Key Usage (EKU). If the attackers compromise a certificate…

Source: https://junglewise.ai/threats/cve-2026-8367-aria2-aria2c-improper-certificate-validation-via-incorrect-eku  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-14  
License: CC BY 4.0 with a link back

CVE-2026-8367 · Severity: medium · CVSS 4.8 · Published 2026-05-13

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.

Technologies: [Aria2](https://junglewise.ai/threats/technologies/aria2). Vendors: [Aria2](https://junglewise.ai/threats/vendors/aria2).

## Quick answers

**Is CVE-2026-8367 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-8367 being exploited in the wild.

**How severe is CVE-2026-8367?** Medium severity, with a CVSS score of 4.8, published 13 May 2026.

**Which products and versions are affected?** aria2 aria2c.

**Is there a fix for CVE-2026-8367?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-8367 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-8367?** Check whether you run Aria2. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## 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.

## References

- [https://www.tenable.com/security/research/tra-2026-38](https://www.tenable.com/security/research/tra-2026-38)

## Related threats

- [aria2 stack-buffer-underflow in IOFile::getLine](https://junglewise.ai/threats/cve-2026-75421-aria2-stack-buffer-underflow-in-iofile-getline)