Several vulnerabilities were discovered in mercurial, an easy-to-use, scalable distributed version control system.
In Mercurial before 4.4.1, it is possible that a specially malformed repository can cause Git subrepositories to run arbitrary code in the form of a .git/hooks/post-update script checked into the repository. Typical use of Mercurial prevents construction of such repositories, but they can be created programmatically.
The mpatch_apply function in mpatch.c in Mercurial before 4.6.1 incorrectly proceeds in cases where the fragment start is past the end of the original data.
mpatch.c in Mercurial before 4.6.1 mishandles integer addition and subtraction.
The mpatch_decode function in mpatch.c in Mercurial before 4.6.1 mishandles certain situations where there should be at least 12 bytes remaining after the current position in the patch data, but actually are not.
Mercurial version 4.5 and earlier contains a Incorrect Access Control (CWE-285) vulnerability in Protocol server that can result in Unauthorized data access. This attack appear to be exploitable via network connectivity. This vulnerability appears to have been fixed in 4.5.1.
Symbolic links and subrepositories could be used defeat Mercurial's path-checking logic and write files outside the repository root.
For Debian 9 stretch, these problems have been fixed in version 4.0-1+deb9u2.
We recommend that you upgrade your mercurial packages.
For the detailed security status of mercurial please refer to its security tracker page at: https://security-tracker.debian.org/tracker/mercurial
Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS