Security Resilience

CVE-2023-53933

S9Y Serendipity 2.4.0

Public PoC
Published
17 December 2025
Modified
24 December 2025
Patch / advisory
View advisory
CVSS Score v4 8.7
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/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
EPSS Score 0.010 63th percentile
Risk Priority 41 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2023-53933 is a high-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability in S9Y Serendipity. Its CVSS base score is 8.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked in the top 37% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SI-3 (Malicious Code Protection) and CM-7 (Least Functionality) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2023-53933 is a remote code execution vulnerability in Serendipity 2.4.0, a PHP-based blogging platform. The flaw allows authenticated attackers to upload malicious PHP files with a .phar extension via the media upload endpoint. These files can contain system command payloads, enabling arbitrary command execution on the affected server. The vulnerability is rated with a CVSS v3.1 base score of 8.8 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) and is associated with CWE-434 (Unrestricted Upload of File with Dangerous Type).

An attacker with low-privilege authenticated access, such as a registered user, can exploit this vulnerability remotely over the network with low complexity and no user interaction required. By crafting and uploading a .phar file containing malicious payloads to the media endpoint, the attacker achieves full remote code execution on the server, potentially leading to high confidentiality, integrity, and availability impacts, including server compromise, data theft, or further lateral movement.

Advisories and related resources, including the Serendipity documentation at https://docs.s9y.org/, a VulnCheck advisory at https://www.vulncheck.com/advisories/serendipity-authenticated-remote-code-execution-via-file-upload, and a public proof-of-concept exploit at https://www.exploit-db.com/exploits/51372, provide further details on the issue. Security practitioners should consult these for recommended mitigations, such as restricting upload permissions or applying any available patches.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

Serendipity 2.4.0 contains a remote code execution vulnerability that allows authenticated attackers to upload malicious PHP files with .phar extension. Attackers can upload files with system command payloads to the media upload endpoint and execute arbitrary commands on the server.

CWE(s)
CWE-434

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001 Data Obfuscation Command And Control
Adversaries may obfuscate command and control traffic to make it more difficult to detect.
attack.mitre.org →
T1001.003 Protocol or Service Impersonation Command And Control
Adversaries may impersonate legitimate protocols or web service traffic to disguise command and control activity and thwart analysis efforts.
attack.mitre.org →
T1003.004 LSA Secrets Credential Access
Adversaries with SYSTEM access to a host may attempt to access Local Security Authority (LSA) secrets, which can contain a variety of different credential materials, such as credentials for service accounts.
attack.mitre.org →
T1003.005 Cached Domain Credentials Credential Access
Adversaries may attempt to access cached domain credentials used to allow authentication to occur in the event a domain controller is unavailable.
attack.mitre.org →
T1007 System Service Discovery Discovery
Adversaries may try to gather information about registered local system services.
attack.mitre.org →
T1011.001 Exfiltration Over Bluetooth Exfiltration
Adversaries may attempt to exfiltrate data over Bluetooth rather than the command and control channel.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-31576Same product: S9Y Serendipity
CVE-2024-58282Same product: S9Y Serendipity
CVE-2026-39971Same product: S9Y Serendipity
CVE-2023-53932Same product: S9Y Serendipity
CVE-2026-39963Same product: S9Y Serendipity
CVE-2023-38098Shared CWE-434
CVE-2024-46479Shared CWE-434
CVE-2024-4389Shared CWE-434
CVE-2026-41517Shared CWE-434
CVE-2024-4345Shared CWE-434

Affected Assets

s9y
serendipity
2.4.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V5.1.1

Mitigating Controls (NIST 800-53 r5) AI

SI-3 Malicious Code Protection good match

Malicious-code protection at entry points blocks dangerous file types from being accepted and executed.

CM-7 Least Functionality partial match

Least functionality restricts the file types and automatic processing capabilities the system will accept.

SC-18 Mobile Code partial match

Mobile-code controls define, authorize, and block unacceptable uploaded code before automatic processing occurs.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-01 partial match
blocks

Hardened configuration baselines can enforce allowed file types and processing rules.

PR.PS-05 partial match
blocks

Restricting execution of unauthorized software directly blocks dangerous uploaded files from running.

PR.PS-06 partial match
blocks

Secure development practices include input validation and file-type restrictions that prevent this weakness.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.5.25 Assessment and decision on information security events partial match
removes

References