#VU56095 Reachable Assertion in Tor - CVE-2021-38385

Vulnerability identifier: #VU56095

Vulnerability risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-38385

CWE-ID: CWE-617

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Tor
Client/Desktop applications / Web browsers

Vendor: tor.eff.org

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a reachable assertion caused by a behavior mismatch between our batch-signature verification code and our single-signature verification code. A remote attacker can trigger assertion failure and perform a denial of service attack.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Tor: 0.3.5.0 - 0.4.6.6

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External links
https://blog.torproject.org/node/2062
https://gitlab.torproject.org/tpo/core/tor/-/issues/40078

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.