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Upgrade to ProDetect YesWiki Formula Calculator Unsafe eval() Remote Code Execution (CVE-2026-52778) in Google Chronicle
YesWiki prior to 4.6.6 exposes an unsafe PHP eval() call in its Formula Calculator feature (BazaR calculated field logic). An unauthenticated or low-privileged attacker can craft a malicious formula expression that is passed directly into eval(), resulting in arbitrary PHP code execution on the underlying web server, or a crafted expression that triggers resource exhaustion / infinite loops causing denial of service. Successful exploitation grants the attacker the privileges of the web server process, enabling webshell deployment, credential theft, and lateral movement.
MITRE ATT&CK
- Tactic
- Initial Access Execution Impact
YARA-L Detection Query
rule yeswiki_formula_eval_rce
{
meta:
author = "df00tech"
description = "Detects exploitation attempts against YesWiki CVE-2026-52778 unsafe eval() in Formula Calculator"
severity = "CRITICAL"
events:
$http.metadata.event_type = "NETWORK_HTTP"
$http.target.url = /(BF_formula|BazaR|formulaire)/ nocase
$http.target.url = /(eval\(|system\(|exec\(|base64_decode|shell_exec)/ nocase
condition:
$http
}Chronicle YARA-L rule detecting HTTP requests to YesWiki formula endpoints containing embedded PHP code execution primitives, matching CVE-2026-52778 exploitation patterns.
Data Sources
Required Tables
False Positives & Tuning
- Authorized red team assessment traffic
- Static analysis tools crawling wiki source for documentation
- False matches from unrelated query parameters containing substring 'eval'
Other platforms for CVE-2026-52778
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate malicious formula eval() payload submission
Expected signal: Web server access log entry showing POST to /?BazaR/formulaire with body containing 'eval(system(' string; PHP error log may show eval() execution or error
- Test 2Simulate DoS payload via infinite loop formula expression
Expected signal: Elevated CPU utilization on the web server host, PHP-FPM worker timeout/kill logs, web access log entry for the formula endpoint request
- Test 3Simulate webshell drop attempt post-exploitation
Expected signal: File creation event under the YesWiki webroot captured by FIM/EDR, web access log entry for the formula endpoint, PHP-FPM process spawning shell command
References (5)
- https://github.com/YesWiki/yeswiki/security/advisories/GHSA-px5m-h76g-p7p8
- https://nvd.nist.gov/vuln/detail/CVE-2026-52778
- https://github.com/YesWiki/yeswiki/commit/dd2bd8fb099de0d21504bda8a810693b3fcb8e52
- https://github.com/YesWiki/yeswiki/releases/tag/v4.6.6
- https://github.com/advisories/GHSA-px5m-h76g-p7p8
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