CVE-2016-5420 Auth bypass in n/a

What is CVE-2016-5420?

CVE-2016-5420 is a high-severity authentication bypass vulnerability in Debian Debian Linux, published on 10 Aug 2016. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

curl and libcurl before 7.50.1 do not check the client certificate when choosing the TLS connection to reuse, which might allow remote attackers to hijack the authentication of the connection by leveraging a previously created connection with a different client certificate.

Weakness: CWE-285

Which versions are affected by CVE-2016-5420?

It affects 3 products.

Products include Debian Debian Linux, Haxx Libcurl, Opensuse Leap.

How do I fix CVE-2016-5420?

Upgrade to a fixed version.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2016-5420 being exploited?

There is no known exploitation of CVE-2016-5420 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2016-5420, CLEANSTART-2026-UL86016, CURL-CVE-2016-5420, DEBIAN-CVE-2016-5420, GHSA-qpjh-642g-hgh8, UBUNTU-CVE-2016-5420.