CyberSecBulletin
CVE-2022-23517NVD status: Modified

rails-html-sanitizer: Inefficient Regular Expression Complexity

Published Updated By the CyberSecBulletin desk

CVE-2022-23517 is a high-severity inefficient regular expression complexity vulnerability in rails-html-sanitizer from Rails, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected rails-html-sanitizer versions: < 1.4.4. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.58% chance of exploitation within 30 days, higher than 76% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Rails Html Sanitizers to 1.4.4 or a later version.
  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
Railsrails-html-sanitizer< 1.4.4Not stated
RubyonrailsRails Html Sanitizersbefore 1.4.41.4.4
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
LowNo special conditions are needed; the attack works reliably.
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
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

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

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

Official description

rails-html-sanitizer is responsible for sanitizing HTML fragments in Rails applications. Certain configurations of rails-html-sanitizer < 1.4.4 use an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption. This issue has been patched in version 1.4.4.

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

The underlying weakness: Inefficient Regular Expression Complexity

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How developers prevent this class of flaw

  • Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
  • Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
  • Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.

More Inefficient Regular Expression Complexity vulnerabilities (CWE-1333)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Inefficient Regular Expression Complexity vulnerabilities

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