Mercurial path-checking Logic Symbolic Link Vulnerability [CVE-2019-3902]

CVE Number – CVE-2019-3902

A vulnerability in Mercurial could allow a local attacker to conduct symbolic link (symlink) attacks on a targeted system. The vulnerability exists because the path-checking logic of the affected software imposes insufficient security restrictions. An attacker could exploit this vulnerability by conducting a symlink attack on a targeted system. A successful exploit could allow the attacker to write files outside of a repository on the system.Mercurial has confirmed the vulnerability and released software updates.


  • To exploit this vulnerability, the attacker must have user-level access to the targeted system. This access requirement may reduce the likelihood of a successful exploit.


  • Administrators are advised to apply the appropriate updates.Administrators are advised to allow only trusted users to access local systems.Administrators are advised to allow only privileged users to access administration or management systems.Administrators are advised to monitor critical systems.

Vendor Announcements

Fixed Software

  • Mercurial has released software updates at the following link: Mercurial 4.9

Jason Davies

UK based technology professional, with an interest in computer security and telecoms.

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