CVE-2024-28850

EUVD-2024-0892 · Published Mar 25, 2024

WP Crontrol vulnerable to possible RCE when combined with a pre-condition

Impact

WP Crontrol includes a feature that allows administrative users to create events in the WP-Cron system that store and execute PHP code subject to the restrictive security permissions documented here. While there is no known vulnerability in this feature on its own, there exists potential for this feature to be vulnerable to RCE if it were specifically targeted via vulnerability chaining that exploited a separate SQLi (or similar) vulnerability.

This is exploitable on a site if one of the below preconditions are met:

The site is vulnerable to a writeable SQLi vulnerability in any plugin, theme, or WordPress core
The site's database is compromised at the hosting level
The site is vulnerable to a method of updating arbitrary options in the wp_options table
The site is vulnerable to a method of triggering an arbitrary action, filter, or function with control of the parameters

Patches

As a hardening measure, WP Crontrol version 1.16.2 ships with a new feature that prevents tampering of the code stored in a PHP cron event.

All PHP cron events are now secured via an integrity check that makes use of an HMAC to store a hash of the code alongside it when the event is saved. When the event runs, the hash is verified to ensure the code has not been tampered with. WP Crontrol will not execute the PHP code if the hash cannot be verified or if a stored hash is not present. If an attacker with database-level access were to modify the code in an event in an attempt to execute arbitrary code, the code would no longer execute.

Any PHP cron events that exist in the database prior to updating to version 1.16.2 will cease to execute until an administrative user re-saves them from the Cron Events screen in the admin area. A notice will be shown in the admin area informing administrative users if this is the case.

Workarounds

Given that one or more of the preconditions listed above are met, there are no known workarounds for this issue other than to update WP Crontrol to version 1.16.2 or later.

Note that neither the DISALLOW_FILE_MODS constant nor the DISALLOW_FILE_EDIT constant prevent this from being exploitable because these constants do not prevent PHP cron events from being executed. It's an intended feature of WP Crontrol that PHP cron events in the database will continue to run according to their schedule even if editing PHP cron events is disabled due to one of these constants being defined.

FAQ

Is my site at risk?

Your site is only at risk if at least one of the preconditions listed above are met and an attacker is actively attacking your site in order to exploit this. There is no known vulnerability in this feature on its own.

Why is this classified as high severity?

The CVSS score is used to classify the severity of a vulnerability in isolation, which in this case is high due to the possibility of RCE. The actual risk is likely to be low and is dependent entirely on one of the preconditions being met.

How is this any different to an SQLi vulnerability that would allow an attacker to create an Administrator user and then access the theme or plugin editor?

The difference is in the handling of the DISALLOW_FILE_MODS and DISALLOW_FILE_EDIT constants. With either one of these constants defined in your wp-config.php file then the plugin and theme editors are disabled. In WP Crontrol the ability to edit PHP cron events in WP Crontrol is also disabled in this case, however PHP cron events in the database will continue to run according to their schedule.

Thanks

This issue was identified by John Blackbourn, the author of the WP Crontrol plugin.

Thanks go to:

Calvin Alkan for researching and reporting many vulnerabilities in WordPress plugins and for publishing the details on the snicco blog. Calvin's work prompted me to investigate whether the PHP cron event functionality in WP Crontrol could be exploited when attacked via with vulnerability chaining, and he collaborated on this security advisory.
Joe Hoyle for collaborating on this advisory.

Technologies

Johnbillion Wp CrontrolJohnbillion Wp-Crontrol

Weaknesses

CWE-494

CVSS scores

v3.18.1CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access Execution Privilege Escalation Lateral Movement Collection

T1068Exploitation for Privilege Escalation T1072Software Deployment Tools T1185Browser Session Hijacking T1195.001Compromise Software Dependencies and Development Tools T1195.002Compromise Software Supply Chain

References

Potentially impacted assets

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Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Two situations are possible. When the decoding is done by your own application or reverse proxy, identify the component and update it. If an update is not possible right away, reject requests with "Content-Encoding: br" at the reverse proxy or WAF. When the asset is hosted on a managed platform or behind a CDN (for example Platform.sh, Upsun or Fastly), the decoding may be done by the provider's edge router, in front of your application. You cannot patch it yourself, but this router handles all the traffic of your site. Ask your provider to confirm that its edge components are patched against CVE-2026-111497. Assets hosted on a managed platform or behind a CDN carry the tag "paas: platform.sh" or "cdn: fastly" in the asset view: for these assets, the Brotli decoding is done by the provider's edge router, in front of your application, and only the provider can patch it. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Contact your edge provider about the status of the pathing (Fastly / Plateform.sh) Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.