CVE-2026-53756

Executive Summary

CVE-2026-53756 is a blind SQL injection vulnerability in Emlog CMS Pro versions prior to 2.6.16, residing in the User_Model::getUserDataByLogin() method. The flaw allows an authenticated attacker with high privileges to extract sensitive data from the underlying database by crafting malicious input passed through the $account parameter, which is directly interpolated into SQL queries without parameterization or filtering.

The vulnerability is reachable via the authentication cookie validation path, where a username extracted from the cookie enters the SQL query unfiltered. Exploitation is constrained by an HMAC signature requirement that necessitates knowledge of the AUTH_KEY secret. The CVSS score of 4.9 (High complexity, High privilege requirement) reflects this constraint. Successful exploitation results in high confidentiality impact — an attacker can enumerate database contents, potentially exposing password hashes, user credentials, and other sensitive application data.

Technical Analysis

The vulnerability exists in the User_Model::getUserDataByLogin() method within Emlog CMS Pro versions prior to 2.6.16. The NVD description indicates that the $account parameter is directly interpolated into SQL queries without any filtering or sanitization — a textbook example of CWE-89 (Improper Neutralization of Special Elements used in an SQL Command).

The attack surface is the authentication cookie validation path. The application extracts a $username value from the authentication cookie and passes it unfiltered into the vulnerable SQL query. This creates a blind SQL injection vector — "blind" indicating that the attacker may not receive direct query output in the response but can infer results through boolean-based or time-based techniques.

Critically, the vulnerability is guarded by an HMAC signature that requires the AUTH_KEY server-side secret to forge. This means that an attacker must either:

1. Possess knowledge of AUTH_KEY (e.g., through a separate information disclosure or configuration leak), or
2. Already possess a valid session and be able to manipulate cookie parameters while maintaining HMAC integrity, or
3. Exploit the injection through a different vector where $account is populated from another source.

The HMAC protection significantly elevates the attack complexity. This is reflected in the CVSS vector's PR:H (High privileges required) component. Without the AUTH_KEY, an attacker cannot simply forge a malicious cookie — the HMAC validation would reject tampered values before they reach the SQL layer.

It is important to note that the exact SQL query structure, surrounding code, and cookie parameter names beyond $username are not detailed in the provided description. Insufficient technical detail is available regarding the precise SQL statement, the database management system in use, and the complete request flow.

The vulnerability affects all Emlog CMS Pro deployments running versions earlier than 2.6.16. Version 2.6.16 contains the patch for this issue.

Exploitation Scenarios

No public PoC or exploit code is available for this vulnerability. The attack chain described below is inferred from the vulnerability class and the details provided in the NVD description.

Scenario: Database Data Exfiltration via Authenticated Blind SQL Injection

Step 1 — Reconnaissance and Target Identification: An attacker first identifies Emlog CMS Pro instances exposed on the internet. This can be accomplished using search engine dorking or network scanning via Shodan queries such as http.html:"Emlog". The attacker fingerprints the exact version through application metadata, error messages, or publicly accessible version disclosure endpoints. Targets running versions earlier than 2.6.16 are flagged as vulnerable.

Step 2 — Establishing the Required Access Level: Because the vulnerability requires PR:H (High privileges), the attacker must first obtain a high-privilege account. This could be achieved through credential stuffing, password spraying against administrator accounts, or leveraging a separate vulnerability (e.g., a previous authentication bypass or configuration leak). Alternatively, the attacker could seek to obtain the AUTH_KEY value from an exposed configuration file or backup file, which would allow HMAC forgery.

Step 3 — Triggering the SQL Injection: Once the attacker has the necessary privileges (or the AUTH_KEY), they craft a malicious value for the $username parameter within the authentication cookie. Because the HMAC guard requires the AUTH_KEY, the attacker must compute a valid HMAC signature over the malicious cookie value. The crafted payload contains SQL injection syntax — for example, injecting boolean conditions or time-delay functions into the username field. Crafted cookies are then submitted to the application's authentication validation endpoint.

Step 4 — Blind Data Extraction: The attacker leverages blind SQL injection techniques to extract database contents character-by-character. Boolean-based techniques involve injecting conditions that alter the application's response behavior (e.g., "if the first character of the admin password hash is 'a', return a valid session"). Time-based techniques use database functions to introduce measurable delays, allowing the attacker to infer query results from response latency. Through iterative queries, the attacker reconstructs sensitive data — password hashes, email addresses, session tokens, or other application data.

Step 5 — Post-Exploitation Impact: With extracted password hashes, the attacker can attempt offline cracking to obtain plaintext credentials for administrator accounts. Successful cracking grants full administrative control of the CMS. The attacker could then deploy web shells, deface the site, pivot to the underlying server, or use compromised CMS credentials for lateral movement into adjacent infrastructure.

No public PoC is available; the attack chain is inferred from the vulnerability class. The high privilege requirement and HMAC guard present meaningful hurdles, but once cleared, the confidentiality impact is substantial.

Impact Assessment

The CVSS base score is 4.9 (Medium severity) with the vector CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N. Breaking down the subscores:

• Attack Vector — Network (AV:N): The vulnerability is exploitable remotely over the network.
• Attack Complexity — Low (AC:L): No special conditions must be met for exploitation beyond the privilege requirement.
• Privileges Required — High (PR:H): The attacker must possess high-privilege credentials or the AUTH_KEY secret to bypass the HMAC guard.
• User Interaction — None (UI:N): No victim interaction is required.
• Confidentiality Impact — High (C:H): Complete database disclosure is possible, including password hashes, user data, and application secrets.
• Integrity Impact — None (I:N): The injection is read-oriented (blind data extraction) and does not directly allow data modification.
• Availability Impact — None (A:N): No denial-of-service impact is indicated.

Business Impact:

The primary business impact is the exposure of sensitive data held within the Emlog CMS database. Given the high confidentiality impact, data such as registered user credentials, personal information, and potentially site configuration secrets could be exposed. If password hashes are cracked, account takeover becomes possible, further enabling content manipulation, malware distribution to site visitors, or reputational damage.

Affected Systems:

All deployments of Emlog CMS Pro running versions prior to 2.6.16 are affected. This includes public-facing websites managed by organizations using the CMS. The influence scope is single-system — the vulnerability does not extend to adjacent systems beyond the target's database server.

Blast Radius:

The blast radius is constrained by the privilege requirements. Exploitation requires either a high-privilege account or the AUTH_KEY secret. Organizations that have not hardened administrator credentials or protected configuration files face greater exposure. Once exploited, the resulting breach could cascade into broader network compromise if the database server is reachable from other internal assets with elevated privileges.

Detection Guidance

Sigma Rule

title: Emlog CMS Pro Blind SQL Injection via Auth Cookie (CVE-2026-53756)
id: 7f7a8d3b-9214-4e8b-a54c-2ef8d9b6f55a
status: experimental
description: Detects potential exploitation attempts of blind SQL injection in Emlog CMS Pro authentication cookie handling
author: Valtersit Threat Intelligence
date: 2026/05/15
logsource:
  category: webserver
  product: generic
detection:
  selection_cookie:
    http.cookie|contains: 'username='
  selection_payload:
    http.cookie|contains|all:
      - 'username='
    http.cookie|re: '(username|account)=[^;]*(\'|%27)+.*(OR|or|AND|and|SELECT|select|SLEEP|sleep|BENCHMARK|BENCHB|WAITFOR|waitfor|IF|if)(\s|%20|\()'
  selection_timebased:
    http.cookie|re: '.*(SLEEP|sleep|BENCHMARK|benchmark|pg_sleep|WAITFOR|waitfor).*'
  condition: selection_cookie and (selection_payload or selection_timebased)
  timeframe: 5m
fields:
  - client.ip
  - server.process.name
  - http.http_user_agent
  - http.url
falsepositives:
  - Legitimate usernames containing SQL keywords (unlikely but possible)
  - Security scanners conducting authorized testing
level: high
tags:
  - attack.t1190
  - attack.t1505.003
  - cve.2026-53756

YARA Rule

rule CVE_2026_53756_Emlog_SQLi_Cookie
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects SQL injection payload patterns targeting Emlog CMS authentication cookie"
        cve = "CVE-2026-53756"
        date = "2026-05-15"
        severity = "high"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-53756"

    strings:
        $sql_string = /(username|account)=\w*(\x27|\x22|\x3B)(--|%23|OR|AND|SLEEP|BENCHMARK|WAITFOR|IF)/
        $blind_bool = /(\x27|\x3B)\s*(OR|AND)\s+\d+\s*=\s*\d+/
        $time_delay = /(SLEEP|BENCHMARK|WAITFOR|pg_sleep)\(\s*\d+/
        $comment_markers = /(\x27--|%27--|\x27#|\x27\x2D\x2D\x20)/
        $cookie_name = /username\s*=\s*[^;]*$/

    condition:
        uint16(0) == 0x3C21 or   // matches HTML or HTTP content
        any of ($sql_string) or
        any of ($blind_bool) or
        any of ($time_delay) or
        (all of ($comment_markers) and any of ($cookie_name))
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-53756 - Emlog CMS Pro Blind SQL Injection Attempt via Authentication Cookie";
    flow:established,to_server;
    http.cookie;
    content:"username=";
    pcre:"/username\s*=\s*[^;\s]*?[\x27|\x22](OR|AND|--|#|SLEEP|BENCHMARK|WAITFOR|IF|SELECT|UNION)/i";
    classtype:attempted-admin;
    sid:202653756;
    rev:1;
    metadata:created_at 2026_05_15, cve CVE_2026_53756, updated_at 2026_05_15;
)

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-53756 - Emlog CMS Pro Time-Based SQL Injection via Authentication Cookie";
    flow:established,to_server;
    http.cookie;
    content:"username=";
    pcre:"/username\s*=\s*[^;\s]*?(SLEEP|BENCHMARK|pg_sleep|WAITFOR|waitfor)\s*\(\s*\d+/i";
    classtype:attempted-admin;
    sid:202653757;
    rev:1;
    metadata:created_at 2026_05_15, cve CVE_2026_53756, updated_at 2026_05_15;
)

Elastic Detection

// Detect HTTP requests with SQL injection patterns in authentication cookie
sequence by client.ip with maxspan=5m
  [ network where event.type == "start" and destination.port == 443 ]
  [ http where
      http.request.cookie : "*username=*" and
      (
        http.request.cookie : "*username=*'*" or
        http.request.cookie : "*username=*%27*"
      ) and
      (
        http.request.cookie : "*(OR|or|AND|and)*" or
        http.request.cookie : "*--*" or
        http.request.cookie : "*#*" or
        http.request.cookie : "*(SLEEP|BENCHMARK|WAITFOR|pg_sleep)*"
      ) and
      http.request.method : "GET" or "POST"
  ]

Splunk SPL Query

index=weblog OR index=proxy OR index=apache
| search http_cookie IN ("*username=*") 
| regex _raw "(?i)(username|account)=[^;\s]*?['\x22](OR|AND|SLEEP|BENCHMARK|WAITFOR|IF|SELECT|UNION|--|#)"
| eval payload_extracted = urldecode(http_cookie)
| eval attack_flags = if(match(payload_extracted, "(?i)(SLEEP\(|BENCHMARK\(|WAITFOR\s+DELAY|pg_sleep\()"), "time-based", 
                        if(match(payload_extracted, "(?i)('\s*(OR|AND)\s+[\d\w]+\s*=\s*[\d\w]+)"), "boolean-based", "unknown"))
| stats count by src_ip, dest_ip, http_url, uri_path, attack_flags, _time
| sort - _time
| where attack_flags != "unknown"
| table _time, src_ip, dest_ip, http_url, attack_flags, count

Wazuh OSSEC Rule

<group name="web,emlog,sql_injection,">
  <!-- CVE-2026-53756: Emlog CMS Pro Blind SQL Injection via Auth Cookie -->

  <rule id="760340" level="12">
    <decoded_as>json</decoded_as>
    <field name="url">\.php</field>
    <field name="cookie" type="pcre2">(?i)username\s*=\s*[^;\s]*?['\x22](OR|AND|SLEEP|BENCHMARK|WAITFOR|IF|SELECT|UNION|--|#)</field>
    <description>CVE-2026-53756: Possible Emlog CMS SQL injection attempt via authentication cookie</description>
    <group>web_attack,sql_injection,emlog,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>

  <rule id="760341" level="14">
    <decoded_as>json</decoded_as>
    <field name="cookie" type="pcre2">(?i)username\s*=\s*[^;\s]*?(SLEEP|BENCHMARK|pg_sleep|WAITFOR)\s*\(\s*\d+</field>
    <description>CVE-2026-53756: Time-based blind SQL injection payload detected in Emlog CMS cookie</description>
    <group>web_attack,sql_injection,emlog,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED

No patch evidence from any tracked source has been identified. The NVD description indicates the issue was patched in version 2.6.16, but no repository commit, advisory, or vendor bulletin confirming this patch availability has been verified through our tracked channels. Treat this vulnerability as actively present in all versions prior to 2.6.16 until vendor confirmation is obtained.

1) Immediate Mitigations (until patch is available and applied)

• Access restriction: Restrict administrative and authentication endpoints to trusted IP ranges using network-level firewalls or Web Application Firewall (WAF) rules. This limits the attack surface to approved networks only.
• Credential hardening: Enforce strong, unique passwords for all high-privilege accounts. Enable multi-factor authentication (MFA) where the CMS or surrounding infrastructure supports it.
• Configuration file protection: Ensure configuration files containing the AUTH_KEY are not accessible via web. Verify file permissions are set to deny read access to web server users (e.g., chmod 600 for the configuration directory).
• Web Application Firewall rules: Deploy WAF rules to inspect cookie values for SQL injection patterns (quotes followed by SQL keywords, time-delay functions). Use the detection rules provided above as template signatures.
• Database privilege reduction: Ensure the CMS database user account operates with the least-privilege principle. The database account should not have administrative rights over the database instance or access to other databases on the same server.
• Monitor authentication logs: Actively review authentication logs for abnormal patterns, including repeated failed logins followed by unusual cookie modification behavior, which may indicate reconnaissance.

2) Patch / Upgrade Steps

• Upgrade Emlog CMS Pro to version 2.6.16 (or later) once the patch is confirmed available from the vendor. The NVD description states the issue has been patched in version 2.6.16.
• Before upgrade, back up the CMS filesystem and database.
• Test the upgrade in a staging environment to verify compatibility with existing plugins, themes, and custom modifications.
• After upgrade, verify the User_Model::getUserDataByLogin() method properly parameterizes SQL queries using prepared statements or parameterized queries to prevent future SQL injection.
• Confirm the HMAC validation logic correctly validates signature integrity over all cookie-derived parameters before SQL execution.

3) Long-Term Hardening

• Web application code review: Audit custom and third-party plugins for similar SQL injection patterns. Emphasize parameterized queries over string concatenation throughout the codebase.
• Security update policy: Establish a repeatable process for tracking and applying Emlog CMS updates within 48 hours of vendor release.
• Database monitoring: Deploy database activity monitoring solutions to flag anomalous queries originating from the CMS application account.
• Secrets management: Move the AUTH_KEY out of source-controlled configuration files. Use environment variables or a dedicated secrets management system.

References

1. NVD Entry for CVE-2026-53756 — https://nvd.nist.gov/vuln/detail/CVE-2026-53756
2. CWE-89: SQL Injection — https://cwe.mitre.org/data/definitions/89.html
3. Emlog CMS Official Site — https://www.emlog.net/ (for vendor patch release announcements and version 2.6.16 download)
4. MITRE ATT&CK — T1190: Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/

Known Threat Actor Campaigns / Exploit-in-the-Wild Evidence:

• CISA KEV Status: This vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog. No in-the-wild exploitation has been confirmed to date.
• Exploit availability: No public proof-of-concept, exploit code, or Nuclei template has been identified. No threat actor campaign has been publicly attributed to exploitation of this CVE.
• EPSS Score: Not yet scored by FIRST.org at the time of this report. Analysts should monitor for EPSS score release to gauge likely exploitation probability.