regex: Inefficient Regular Expression Complexity
CVE-2022-24713 is a high-severity inefficient regular expression complexity vulnerability in regex from Rust-lang, 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 regex versions: < 1.5.5. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 14.5% chance of exploitation within 30 days, which is in the top 3.32% of all scored CVEs.
EPSS places it among the vulnerabilities most likely to be exploited soon.
What to do
- Check which version of regex you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Rust-lang | regex | < 1.5.5 | Not stated |
| Fedora Project | Fedora | 34; 35; 36 | Not stated |
| Debian | Debian Linux | 9.0; 10.0; 11.0 | Not 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 system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CNA (github.com) |
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 2.0 | 5.0 | Medium | NVD |
Official description
regex is an implementation of regular expressions for the Rust language. The regex crate features built-in mitigations to prevent denial of service attacks caused by untrusted regexes, or untrusted input matched by trusted regexes. Those (tunable) mitigations already provide sane defaults to prevent attacks. This guarantee is documented and it's considered part of the crate's API. Unfortunately a bug was discovered in the mitigations designed to prevent untrusted regexes to take an arbitrary amount of time during parsing, and it's possible to craft regexes that bypass such mitigations. This makes it possible to perform denial of service attacks by sending specially crafted regexes to services accepting user-controlled, untrusted regexes. All versions of the regex crate before or equal to 1.5.4 are affected by this issue. The fix is include starting from regex 1.5.5. All users accepting user-controlled regexes are recommended to upgrade immediately to the latest version of the regex crate. Unfortunately there is no fixed set of problematic regexes, as there are practically infinite regexes that could be crafted to exploit this vulnerability. Because of this, it us not recommend to deny known problematic regexes.
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
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/rust-lang/regex/security/advisories/GHSA-m5pq-gvj9-9vr8Third Party Advisory
Patches and release notes
- github.com/rust-lang/regex/commit/ae70b41d4f46641dbc45c7a4f87954aea356283eThird Party Advisory
Third-party and government advisories
- groups.google.com/g/rustlang-security-announcements/c/NcNNL1Jq7YwThird Party Advisory
- lists.debian.org/debian-lts-announce/2022/04/msg00003.htmlMailing List, Third Party Advisory
- lists.debian.org/debian-lts-announce/2022/04/msg00009.htmlMailing List, Third Party Advisory
- security.gentoo.org/glsa/202208-08Third Party Advisory
- security.gentoo.org/glsa/202208-14Third Party Advisory
- debian.org/security/2022/dsa-5113Third Party Advisory
- debian.org/security/2022/dsa-5118Third Party Advisory
Other references
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JANLZ3JXWJR7FSHE57K6…
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/O3YB7CURSG64CIPCDPNM…
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PDOWTHNVGBOP2HN27PUF…
Recent Inefficient Regular Expression Complexity vulnerabilities
- 7.5 High severity
- 7.5 High severity
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