Huge backdoor discovered that could compromise SSH logins on Linux

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On Friday March 29, Microsoft employee Andres Freund shared that he had found odd symptoms in the xz package on Debian installations. Freund noticed that ssh login was requiring a lot of CPU and decided to investigate leading to the discovery.

The vulnerability has received the maximum security ratings with a CVS score of 10 and a Red Hat Product Security critical impact rating.

Red Hat assigned the issue CVE-2024-3094 but based on the severity and a previous major bug being named Heartbleed, the community has cheekily named the vulnerability a more vulgar name and inverted the Heartbleed logo.

Luckily the vulnerability has been caught early

Red Hat wrote: “Malicious code was discovered in the upstream tarballs of xz, starting with version 5.6.0. Through a series of complex obfuscations, the liblzma build process extracts a prebuilt object file from a disguised test file existing in the source code, which is then used to modify specific functions in the liblzma code. This results in a modified liblzma library that can be used by any software linked against this library, intercepting and modifying the data interaction with this library.”

The malicious injection can be found only in the tarball download package of xz versions 5.6.0 and 5.6.1 libraries. The Git distribution does not include the M4 Macro that triggers the code. The second-stage artifacts are present in the Git repository for the injection during the build time, if the malicious M4 macro is present. Without the merge into the build, the 2nd-stage file is innocuous.

You are recommended to check for xz version 5.6.0 or 5.6.1 in the following distributions and downgrade to 5.4.6. If you cannot you should disable public facing SSH servers.