article HN

• Backdoor in upstream xz/liblzma leading to SSH server compromise - The upstream xz repository and the xz tarballs have been backdoored.
  • found using valgrind - backdoor not present in version control - but in the binary files used to “test” the xz binary
    • Timeline of XZ attack / HN
    • The xz attack shell script
  • xz used in openssh cli
  • the apparent author of the backdoor… has been part of the xz project for 2 years… and to be honest with this level of sophistication I would be suspicious of even older versions of xz until proven otherwise.
• (1) safe interoperability among xz implementations is not guaranteed;
• (2) xz’s extensibility is unreasonable and problematic;
• (3) xz is vulnerable to unprotected flags and length fields;
• (4) LZMA2 is unsafe and less efficient than the original LZMA;
• (5) xz includes useless features that increase the number of false positives for corruption;
• (6) xz shows inconsistent behavior with respect to trailing data;
• (7) error detection in xz is several times less accurate than in bzip2, gzip and lzip.