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Serendipity CMS CVE-2026-73628

| EUVDEUVD-2026-57797 MEDIUM
Cross-site Scripting (XSS) (CWE-79)
2026-08-13 VulnCheck GHSA-4g8w-wg6x-gvqc
PHP XSS Serendipity
5.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
5.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
6.1 MEDIUM

Network-delivered reflected XSS; no privileges needed; user interaction required; scope changes as JavaScript executes in victim browser context.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

1
Analysis Generated
Aug 13, 2026 - 12:36 vuln.today

DescriptionCVE.org

Serendipity versions >= 2.3.5 and <= 2.6.0 contain a reflected cross-site scripting vulnerability in the search clean-URL route (/search/<term>). In include/functions_routing.inc.php serveSearch(), the sanitisation pipeline runs urldecode() after HTML-encoding, so a single URL-encoded HTML payload survives strip_tags() and htmlspecialchars() and is then decoded back into live HTML in the page. A crafted search link can execute arbitrary JavaScript in the victim's browser. Fixed in 2.6.1.

AnalysisAI

Reflected cross-site scripting in Serendipity CMS versions 2.3.5 through 2.6.0 enables arbitrary JavaScript execution in a victim's browser via the clean-URL search route. The flaw in include/functions_routing.inc.php's serveSearch() inverts the sanitization order - urldecode() runs after htmlspecialchars() and strip_tags(), so a URL-encoded payload survives HTML encoding intact and is decoded back into executable markup before page rendering. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft URL-encoded XSS payload in search path
Delivery
Distribute crafted link via phishing or embedded referral
Exploit
Victim clicks link with active site session
Execution
urldecode() expands payload after HTML encoding
Persist
Script tag renders in browser page
Impact
Session cookie or credentials exfiltrated to attacker
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target Serendipity installation is running a version between 2.3.5 and 2.6.0 inclusive, and that the clean-URL routing mode is active so that the /search/<term> route is handled by serveSearch() in include/functions_routing.inc.php - the vulnerable decode-after-encode pipeline only exists in that code path. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 base score of 5.3 reflects a medium-severity, network-accessible flaw that requires victim interaction (UI:P) - a meaningful constraint that limits opportunistic mass exploitation. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker constructs a URL of the form https://target-site.example/search/%3Cscript%3Ealert(document.cookie)%3C%2Fscript%3E and delivers it to a logged-in Serendipity administrator via a phishing email or embedded link. When the administrator clicks the link, the application decodes the payload after sanitization, rendering the script tag in the page and exfiltrating the session cookie to an attacker-controlled host. …
Remediation Upgrade Serendipity to version 2.6.1, which corrects the sanitization pipeline in include/functions_routing.inc.php so that urldecode() is applied before HTML-encoding functions rather than after. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-73628 vulnerability details – vuln.today
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