CyberSecBulletin
CVE-2022-31163NVD status: Modified

tzinfo: Improper Limitation of a Pathname to a Restricted Directory

Published Updated By the CyberSecBulletin desk

CVE-2022-31163 is a high-severity improper limitation of a pathname to a restricted directory vulnerability in tzinfo, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected tzinfo versions: < 0.3.61; >= 1.0.0, < 1.2.10. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 2.45% chance of exploitation within 30 days, higher than 85% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Check which version of tzinfo you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on github.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Tzinfotzinfo< 0.3.61; >= 1.0.0, < 1.2.10Not stated
DebianDebian Linux10.0Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
HighSuccess depends on conditions outside the attacker's control.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.5HighCNA (github.com)
CVSS 3.18.1HighNVD

Official description

TZInfo is a Ruby library that provides access to time zone data and allows times to be converted using time zone rules. Versions prior to 0.36.1, as well as those prior to 1.2.10 when used with the Ruby data source tzinfo-data, are vulnerable to relative path traversal. With the Ruby data source, time zones are defined in Ruby files. There is one file per time zone. Time zone files are loaded with `require` on demand. In the affected versions, `TZInfo::Timezone.get` fails to validate time zone identifiers correctly, allowing a new line character within the identifier. With Ruby version 1.9.3 and later, `TZInfo::Timezone.get` can be made to load unintended files with `require`, executing them within the Ruby process. Versions 0.3.61 and 1.2.10 include fixes to correctly validate time zone identifiers. Versions 2.0.0 and later are not vulnerable. Version 0.3.61 can still load arbitrary files from the Ruby load path if their name follows the rules for a valid time zone identifier and the file has a prefix of `tzinfo/definition` within a directory in the load path. Applications should ensure that untrusted files are not placed in a directory on the load path. As a workaround, the time zone identifier can be validated before passing to `TZInfo::Timezone.get` by ensuring it matches the regular expression `\A[A-Za-z0-9+\-_]+(?:\/[A-Za-z0-9+\-_]+)*\z`.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Limitation of a Pathname to a Restricted Directory

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

How developers prevent this class of flaw

  • For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
  • Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

More Improper Limitation of a Pathname to a Restricted Directory vulnerabilities (CWE-22)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Improper Limitation of a Pathname to a Restricted Directory vulnerabilities

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