---
title: "CVE-2026-52778: YesWiki has Unsafe eval() in its Formula Calculato, Leading to Remote Code Execution & Denial of Service"
url: https://erroneo.us/security/cve/CVE-2026-52778/
description: "CVE-2026-52778 (yeswiki/yeswiki (Composer (PHP))): YesWiki is a wiki system written in PHP. Prior to version 4.6.6, an unsafe execution vulnerability exists…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-08
date_modified: 2026-07-09
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-52778"
kev: false
cvss: 9.8
epss: 0.00798
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-52778: YesWiki has Unsafe eval() in its Formula Calculato, Leading to Remote Code Execution & Denial of Service

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.8% , percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes yeswiki/yeswiki (Composer (PHP)) < 4.6.6, fixed in 4.6.6 . Check your lockfile, including transitive dependencies.

## What it is

YesWiki is a wiki system written in PHP. Prior to version 4.6.6, an unsafe execution vulnerability exists in the Bazar form field calculator (CalcField.php) of YesWiki. The application attempts to sanitize user-defined mathematical formulas using a complex recursive regular expression before passing them to the PHP eval() function. This implementation is inherently flawed: it is vulnerable to Regular Expression Denial of Service (ReDoS / Stack Overflow) which can crash the server, and it creates a high-risk architecture where any logic bypass directly results in arbitrary PHP code execution. Version 4.6.6 patches the issue.

## Affected packages

- Composer (PHP) `yeswiki/yeswiki` < 4.6.6 → fixed: 4.6.6

## Affected products (CVE record)

- YesWiki yeswiki: < 4.6.6

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.80% probability of exploitation activity in the next 30 days; percentile 56.

## Sources

- [GitHub Advisory GHSA-px5m-h76g-p7p8](https://github.com/advisories/GHSA-px5m-h76g-p7p8)
- [CVE.org record CVE-2026-52778](https://www.cve.org/CVERecord?id=CVE-2026-52778)
- [NVD entry CVE-2026-52778](https://nvd.nist.gov/vuln/detail/CVE-2026-52778)
- [github.com](https://github.com/YesWiki/yeswiki/security/advisories/GHSA-px5m-h76g-p7p8)
- [github.com](https://github.com/YesWiki/yeswiki/commit/dd2bd8fb099de0d21504bda8a810693b3fcb8e52)
- [github.com](https://github.com/YesWiki/yeswiki/releases/tag/v4.6.6)

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Source page: https://erroneo.us/security/cve/CVE-2026-52778/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt