A curl security update has been released for Ubuntu Linux 18.04 LTS.

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Ubuntu Security Notice USN-5079-3
September 21, 2021

curl vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS

Summary:

USN-5079-1 introduced a regression in curl.

Software Description:
- curl: HTTP, HTTPS, and FTP client and client libraries

Details:

USN-5079-1 fixed vulnerabilities in curl. One of the fixes introduced a
regression on Ubuntu 18.04 LTS. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

It was discovered that curl incorrect handled memory when sending data to
an MQTT server. A remote attacker could use this issue to cause curl to
crash, resulting in a denial of service, or possibly execute arbitrary
code. (CVE-2021-22945)
Patrick Monnerat discovered that curl incorrectly handled upgrades to TLS.
When receiving certain responses from servers, curl would continue without
TLS even when the option to require a successful upgrade to TLS was
specified. (CVE-2021-22946)
Patrick Monnerat discovered that curl incorrectly handled responses
received before STARTTLS. A remote attacker could possibly use this issue
to inject responses and intercept communications. (CVE-2021-22947)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS:
curl 7.58.0-2ubuntu3.16
libcurl3-gnutls 7.58.0-2ubuntu3.16
libcurl3-nss 7.58.0-2ubuntu3.16
libcurl4 7.58.0-2ubuntu3.16

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-5079-3
  https://ubuntu.com/security/notices/USN-5079-1
  https://launchpad.net/bugs/1944120

Package Information:
  https://launchpad.net/ubuntu/+source/curl/7.58.0-2ubuntu3.16