CVE-2026-88798

Really Simple Security (Free) <= 9.8.2 - Unauthenticated Unbounded Option Growth

2026-09-16 00:00
Naoki Kawahigashi

Strategic Overview

Status
Patched in 9.8.3
Affected Plugin
Really Simple Security – Simple and Performant Security (formerly Really Simple SSL)
Affected Version
<= 9.8.2
CVSS
5.3Medium
Weakness type
CWE-400 · Uncontrolled Resource Consumption
CVE
CVE-2026-88798
View all Really Simple Security – Simple and Performant Security (formerly Really Simple SSL) vulnerabilities

At a glance

CVE-2026-88798 is a medium-severity Uncontrolled Resource Consumption vulnerability in the Really Simple Security WordPress plugin, affecting versions <= 9.8.2. It carries a CVSS score of 5.3 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 9.8.3; sites on affected versions should update now. Disclosed September 2026, reported by Naoki Kawahigashi.

Vulnerability Overview

The Really Simple Security (Free) plugin for WordPress is vulnerable to Denial of Service in all versions up to, and including, 9.8.2. This is due to missing validation on client-supplied IP headers used as storage keys in the rsssl_404_cache option, allowing arbitrary values from HTTP_CLIENT_IP and HTTP_X_FORWARDED_FOR to be written as array keys without bound. This makes it possible for unauthenticated attackers to grow the rsssl_404_cache option without bound by supplying arbitrary values in spoofed client IP headers, degrading site performance when handling 404 responses.

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site, and no interaction from a victim user.

CWE-400: Uncontrolled Resource Consumption

Reaching this weakness in Really Simple Security <= 9.8.2 takes no account at all. Uncontrolled resource consumption means a request can make the server do an amount of work it never bounds, because the size or repetition of the job is taken from the request rather than capped by the code.

A single caller can hold PHP workers, database connections or disk open long enough to slow the site for everyone, without needing any account or any other flaw. For Really Simple Security the fix is 9.8.3: builds <= 9.8.2 are affected, anything from 9.8.3 onward is not.

Remediation

Update to version 9.8.3, or a newer patched version

How does WordSec protect against this?

Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Really Simple Security 9.8.3 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Login Security
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-88798https://www.wordfence.com/threat-intel/vulnerabilities/id/fbfd334c-dba4-49ec-b854-59e52236fe57https://nvd.nist.gov/vuln/detail/CVE-2026-88798

Related records

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