mybb: Improper Control of Generation of Code
CVE-2022-24734 is a high-severity improper control of generation of code vulnerability in mybb, with a CVSS 3.1 base score of 7.2 out of 10. It can be exploited remotely over the network by an attacker with administrator privileges, without any action from a user. Affected mybb versions: >= 1.2.0, < 1.8.30. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 77.8% chance of exploitation within 30 days, which is in the top 0.42% of all scored CVEs.
Exploitation in the next 30 days is more likely than not, according to EPSS.
What to do
- Check which version of mybb 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.
Affected products and versions
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
- HighAdministrator-level access is required first.
- 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:L/PR:H/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.2 | High | CNA (github.com) |
| CVSS 3.1 | 7.2 | High | NVD |
| CVSS 2.0 | 6.5 | Medium | NVD |
Official description
MyBB is a free and open source forum software. In affected versions the Admin CP's Settings management module does not validate setting types correctly on insertion and update, making it possible to add settings of supported type `php` with PHP code, executed on on _Change Settings_ pages. This results in a Remote Code Execution (RCE) vulnerability. The vulnerable module requires Admin CP access with the `Can manage settings?` permission. MyBB's Settings module, which allows administrators to add, edit, and delete non-default settings, stores setting data in an options code string ($options_code; mybb_settings.optionscode database column) that identifies the setting type and its options, separated by a new line character (\n). In MyBB 1.2.0, support for setting type php was added, for which the remaining part of the options code is PHP code executed on Change Settings pages (reserved for plugins and internal use). MyBB 1.8.30 resolves this issue. There are no known workarounds.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Control of Generation of Code
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
How developers prevent this class of flaw
- Refactor your program so that you do not have to dynamically generate code.
- Run your code in a jail or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your product. Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
- Use dynamic tools and techniques that interact with the product using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The product's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
More Improper Control of Generation of Code vulnerabilities (CWE-94)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/mybb/mybb/security/advisories/GHSA-876v-gwgh-w57fThird Party Advisory
- mybb.com/versions/1.8.30/Release Notes
- zerodayinitiative.com/advisories/ZDI-22-503/Third Party Advisory, VDB Entry
Patches and release notes
- github.com/mybb/mybb/commit/92012b9831b330714b9f9b4646a98784113489c1Third Party Advisory
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/167082/MyBB-1.8.29-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/167333/MyBB-Admin-Control-Remote-Code-Execution.htmlExploit, Third Party Advisory
Other vulnerabilities in mybb
- 9.3 Critical severity
- 9.8 Critical severity
- 8.7 High severity
- 8.7 High severity
- 8.8 High severity
- 7.2 High severity
Recent Improper Control of Generation of Code vulnerabilities
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
Spotted an error? Tell us.