CVE-2026-76213

Executive Summary

CVE-2026-76213 is a brute-force protection bypass vulnerability in phpMyFAQ prior to version 4.1.7, specifically affecting the two-factor authentication (2FA) TOTP verification step. The flaw allows an attacker who possesses a valid password to enumerate TOTP codes without being permanently locked out, because the failure counter is scoped to the server-side session and resets whenever the attacker re-authenticates with the stolen password. This effectively renders the five-attempt rate limit meaningless, enabling unbounded guessing of the 6-digit TOTP code. With a CVSS score of 7.4 (High), the vulnerability compromises both confidentiality and integrity of affected phpMyFAQ installations, although successful exploitation requires prior knowledge of a valid password and the capability to obtain fresh session cookies. At the time of this writing, no public proof-of-concept or exploit code has been identified, and no patch evidence has been verified from any tracked source.

Technical Analysis

The vulnerability resides in the two-factor authentication enforcement mechanism of phpMyFAQ versions prior to 4.1.7. The NVD description indicates that the failure counter used to limit TOTP guessing attempts is bound to the user's HTTP session rather than to the user account or the underlying credential pair (password + TOTP secret). This architectural decision creates a critical flaw: session-scoped state can be trivially discarded by the attacker.

The attack mechanism operates as follows. When a user initiates login with a valid username and password, phpMyFAQ creates a session and transitions to the 2FA challenge step, where the user must supply the current TOTP code. The application tracks the number of failed TOTP attempts in a counter associated with that session. After five consecutive failures, the application should terminate the login flow and enforce a lockout. However, because the counter resides in session state, an attacker can simply abandon the current session, obtain a new session cookie, and re-authenticate with the same valid password. The new session starts with a fresh counter at zero, resetting the attempt budget.

This flaw is a classic misinterpretation of the CWE-307 (Improper Restriction of Excessive Authentication Attempts) requirement. For rate limiting to be effective against credential-guessing attacks, the lockout counter must be keyed to a persistent identifier — such as the user account, the source IP address, or a combination of both — rather than to a transient session identifier that the attacker controls. Because the counter is session-scoped, the five-attempt restriction only limits consecutive failures within a single session, not total failures across multiple sessions.

The TOTP (Time-based One-Time Password) standard, as defined in RFC 6238, produces a 6-digit code valid for a 30-second window. For a 6-digit numeric code, the keyspace is 1,000,000 possible values. Without any rate limiting, an attacker could theoretically brute-force the TOTP code in an average of 500,000 attempts. In practice, the 30-second validity window imposes a real-world constraint. However, the vulnerability removes the lockout mechanism that would otherwise make such brute-force attacks infeasible, reducing the effective security to the TOTP keyspace alone. At approximately 5 attempts per second (a conservative rate for HTTP requests), a full keyspace sweep would take roughly 55 hours, but with 30-second window resets, the attacker would need to time attempts within each window. The realistic attack duration is bounded by network latency and the attacker's ability to align attempts with TOTP windows, making a successful guess achievable within hours to days depending on infrastructure.

The attack surface is the HTTP login endpoint that accepts username, password, and TOTP code. No specific URL endpoints or parameter names are provided in the NVD description, and we do not infer them. The vulnerability class is "authentication bypass via inadequate rate limiting," and the specific trigger is the interaction between session cookie management and the 2FA challenge flow.

It is important to note the CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. The high attack complexity (AC:H) reflects the requirement that the attacker must already possess a valid password and must be able to repeatedly obtain fresh session cookies. The privileges-required score of NONE (PR:N) indicates that no account privileges are needed beyond the compromised password. The impact is High for both confidentiality and integrity, reflecting that a successful TOTP bypass grants full authenticated access to the phpMyFAQ application, exposing sensitive FAQ data and potentially allowing content modification. Availability impact is None.

Exploitation Scenarios

The following attack chain is inferred from the vulnerability class and the NVD description. No public PoC exists, and the description provides no specific endpoint details; therefore, implementation-specific steps are described at the class level.

Step 1 — Reconnaissance and Target Identification: The attacker identifies internet-facing phpMyFAQ installations. phpMyFAQ is a popular open-source FAQ system written in PHP, commonly deployed on shared hosting and corporate intranets. The attacker can use search engines or shodan-style queries for "phpMyFAQ" banners, login pages, or distinctive page titles. The attacker then fingerprints the exact version to confirm it is prior to 4.1.7 and therefore vulnerable.

Step 2 — Credential Acquisition: The attacker must obtain a valid username and password. This could be achieved through phishing, credential stuffing using previously leaked databases, or exploiting a separate vulnerability. This step is a prerequisite and is outside the scope of CVE-2026-76213 itself, but it explains the High attack complexity in the CVSS score.

Step 3 — Triggering the Flaw: With valid credentials in hand, the attacker initiates the login process. After entering the correct username and password, the application presents the 2FA challenge. The attacker begins submitting TOTP codes, and after five incorrect attempts, the session-scoped counter reaches its limit. Instead of being locked out, the attacker discards the current session cookie, requests a new session (e.g., by clearing cookies and re-authenticating with the same password), and resumes TOTP guessing. This loop can be automated with a simple script that re-authenticates after every five failures.

Step 4 — Exploitation and Post-Exploitation Impact: Once the correct TOTP code is guessed, the attacker successfully completes the 2FA challenge and gains authenticated access to the phpMyFAQ instance. The attacker now possesses full application-level access, equivalent to the legitimate account holder. Impact includes: reading all FAQ entries, including any confidential or internal documentation stored in the FAQ database; modifying or deleting FAQ content, defacing the public-facing FAQ pages; and potentially extracting sensitive data if the FAQ system stores user data, email addresses, or internal knowledge. If the phpMyFAQ application has administrative features and the compromised account has admin privileges, the attacker could potentially modify application settings, upload files (if the application supports attachments), or pivot to further compromise of the underlying server.

The attack is entirely network-based and can be executed remotely. The lack of rate limiting at the session level means there is no practical lockout threshold. The only remaining defense is the inherent difficulty of guessing a 6-digit TOTP code within the 30-second validity window — a barrier that is measurable but surmountable with automation.

Impact Assessment

From a business perspective, CVE-2026-76213 represents a significant risk to organizations that deploy phpMyFAQ as a knowledge management or customer support platform. The vulnerability effectively neutralizes the second factor of authentication, reducing 2FA to a single factor (password) with a time delay proportional to the attacker's guessing speed. For any organization that relies on phpMyFAQ to protect internal documentation, customer data, or proprietary knowledge, the confidentiality impact is High — an attacker who compromises a single password can eventually gain full access.

The integrity impact is equally High. Successful exploitation allows the attacker to modify FAQ content, potentially injecting misleading information that could mislead customers or employees, or deleting critical documentation. For FAQ systems used in regulated industries, this could have compliance and legal ramifications. The availability impact is scored as None (A:N) in the CVSS vector, because the attack itself does not deny service; however, a determined attacker could delete content, effectively degrading the availability of the knowledge base.

The blast radius is constrained by the requirement for a valid password. This is not a zero-click or unauthenticated vulnerability. However, in the context of credential stuffing campaigns — where attackers routinely test millions of leaked password pairs against web applications — the marginal cost of adding TOTP guessing to an automated attack is low. The CVSS subscores (C:H/I:H/A:N) underpin a risk severity of 7.4 (High). The attack complexity of High (AC:H) tempers the score; if a simpler vector existed that did not require password acquisition, this would likely be a Critical-severity finding.

The affected user base includes all phpMyFAQ installations running versions prior to 4.1.7. The vendor has not published a CVE-specific advisory in the tracked sources, but the fix is included in the 4.1.7 release. No CVSS Environmental Score has been assessed by the reporter; organizations should consider their own exposure — particularly whether their phpMyFAQ instance is internet-facing and whether user accounts are protected by strong, unique passwords that are unlikely to appear in credential-stuffing lists.

Detection Guidance

Detection of this vulnerability is challenging because the exploitation pattern — repeated HTTP POST requests with varying TOTP codes interspersed with new session creations — can resemble legitimate user behavior (e.g., a user mistyping their phone's code). However, there are distinguishing signals: a high volume of 2FA failures followed by session renewal, and a sustained ratio of failures to successes from a single source IP. The following detection rules target these patterns.

Sigma Rule

title: phpMyFAQ TOTP Brute-Force Attempt with Session Reset
id: 0db5b57e-6b9a-4f8c-9f1e-2b4d7a4e90c1
status: experimental
description: Detects repeated failed TOTP authentication attempts in phpMyFAQ followed by session renewal, indicating brute-force bypass of the 2FA rate limit.
author: Valtersit Threat Intelligence
date: 2026-01-15
logsource:
  category: application
  product: phpmyfaq
  definition: Requires application-level audit logs that record failed 2FA attempts with corresponding session IDs.
detection:
  selection:
    event_type: '2fa_failed'
  timeframe: 5m
  condition: selection | count() by source_ip > 5
  filter:
    event_type: '2fa_failed'
    disable_reason: null
  condition2: selection and filter | count() by source_ip, session_id > 5
falsepositives:
  - Users with damaged or misconfigured authenticator apps repeatedly entering wrong codes
  - Automated testing scripts
level: medium
tags:
  - attack.t1110
  - cve.2026.76213
  - cwe.307

YARA Rule

rule phpMyFAQ_TOTP_BruteForce_Logs
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects log entries indicative of repeated TOTP failures in phpMyFAQ"
        cve_id = "CVE-2026-76213"
        date = "2026-01-15"
        severity = "medium"
    strings:
        $a = "2FA failed" ascii wide nocase
        $b = "totp" ascii wide nocase
        $c = "invalid code" ascii wide nocase
        $d = "failed attempt" ascii wide nocase
        $e = "authentication required" ascii wide nocase
        $f = "two-factor" ascii wide nocase
    condition:
        2 of them
}

Note: The YARA rule targets log file patterns; the exact strings depend on phpMyFAQ's logging format, which is not fully disclosed in the description. Analysts should adjust the strings to match their observed log syntax.

Suricata IDS Rule

alert http any any -> any any (msg:"Potential phpMyFAQ TOTP Brute-Force with Session Reset"; flow:established,to_server; content:"POST"; http_method; content:"login"; http_uri; nocase; content:"totp"; http_client_body; nocase; threshold:type threshold, track by_src, count 6, seconds 60; classtype:attempted-admin; sid:202676213; rev:1;)

Note: The rule triggers on HTTP POST requests containing "login" in the URI and "totp" in the body, with a threshold of 6 hits per source IP per 60 seconds. This is a generic approximation; organizations should adjust URI and body keywords to match their phpMyFAQ deployment's actual request format.

Elastic Detection

sequence by source.ip with maxspan=10m
  [ authentication where event.outcome == "failure" and process.name == "*phpmyfaq*" and message like "*totp*" ]
  [ authentication where event.outcome == "success" and process.name == "*phpmyfaq*" and message like "*password*" ]

Note: This EQL rule detects a sequence where a TOTP failure is followed by a successful password re-authentication within 10 minutes, capturing the session-reset pattern central to this vulnerability. Event mapping assumes the logs are ingested with ECS field names (source.ip, event.outcome, etc.).

Splunk SPL Query

index=web sourcetype="phpmyfaq:access" 
| where like(message, "%totp%") AND like(message, "%fail%")
| bucket _time span=5m
| stats count as failures by _time, src_ip, session_id
| where failures > 5
| table _time, src_ip, session_id, failures

Wazuh OSSEC Rule

<group name="phpmyfaq,">
  <rule id="100311" level="10">
    <decoded_as>json</decoded_as>
    <field name="event_type">2fa_failed</field>
    <field name="source_ip" type="pcre2">\d+\.\d+\.\d+\.\d+</field>
    <description>phpMyFAQ: Repeated TOTP authentication failures - possible brute-force bypass</description>
    <options>no_full_log</options>
    <group>authentication_failures,</group>
  </rule>
</group>

Note: The Wazuh rule requires that the json decoder maps the event_type and source_ip fields from the phpMyFAQ access logs. Adjust the field names to match the actual log format used in the environment.

Mitigation & Patch Guidance

Patch Status: Patch confidence is 0/4 — no patch evidence from any tracked source has been verified. The NVD description indicates that the fix is available in phpMyFAQ version 4.1.7 (i.e., versions prior to 4.1.7 are vulnerable). The vendor has not published a formal security advisory in the indices checked for this report, and there are no workarounds documented by the vendor. Organizations should verify the availability of version 4.1.7 or later and prioritize upgrading.

Immediate Mitigations (while unpatched):

1. Disable TOTP 2FA temporarily if business constraints permit. If TOTP is not mandatory for your environment, disabling it removes the vulnerable attack surface entirely — the counter-reset flaw is only exploitable during the 2FA challenge step.
2. Enforce IP-based rate limiting at the network or WAF layer. Deploy a web application firewall or reverse-proxy rule that limits the number of authentication requests per source IP address to a low threshold (e.g., 10 requests per minute). This compensates for the missing application-level lockout. Note that this is imperfect (attackers can rotate IPs) but raises the cost of attack.
3. Enable strong password policies and enforce MFA for all accounts. Since the attack requires a valid password, ensuring that passwords are unique, strong, and not reused across sites reduces the likelihood of an attacker possessing a valid credential in the first place.
4. Monitor for the detection patterns described above. Specifically alert on more than 5 failed TOTP attempts from a single source IP followed by a successful re-authentication within a short window. This is the signature of the session-reset attack.
5. Restrict access to the phpMyFAQ login page using network-level access control lists, VPN requirements, or IP allowlisting, especially for administrative accounts with access to sensitive content.

Patch/Upgrade Steps:

1. Verify the current phpMyFAQ version (phpMyFAQ version can be identified from the admin dashboard or the version.php file).
2. If running a version prior to 4.1.7, schedule an upgrade to 4.1.7 or the latest stable release. The upgrade process typically involves replacing the application files and running a database migration.
3. Before upgrading, take a full backup of the application files and database.
4. After upgrade, verify the 2FA flow: confirm that 5 failed TOTP attempts now result in a lockout that persists even after session renewal (i.e., the counter should be keyed to the user account, not the session).

Long-Term Hardening:

1. Risk-based authentication: Implement additional CAPTCHA or progressive delay mechanisms after 2–3 failed TOTP attempts, regardless of session renewal.
2. Lockout keyed to persistent identifiers: Configure the application (as available in 4.1.7+) to key failure counters to the username + source IP combination, and enforce a lockout duration (e.g., 15 minutes) after exceeding the threshold.
3. Account compromise monitoring: Integrate phpMyFAQ authentication logs into your SIEM and build detections for credential-stuffing patterns (high failure rates across many usernames from one IP, or one username from many IPs).
4. Alternative 2FA methods: Evaluate moving to WebAuthn/FIDO2 hardware keys or push-based MFA, which are not susceptible to offline TOTP guessing. This reduces the impact of any future rate-limit bypass.

References

1. NVD Entry for CVE-2026-76213: https://nvd.nist.gov/vuln/detail/CVE-2026-76213 — Mitre Corporation; the primary source for the vulnerability description and CVSS scoring.
2. phpMyFAQ Official Project & Release Notes: https://www.phpmyfaq.de/ — Official phpMyFAQ website; release notes for version 4.1.7 should document the brute-force fix. (Note: No formal CVE-specific advisory has been located at the time of writing; analysts should verify.)
3. MITRE ATT&CK Technique T1110 — Brute Force: https://attack.mitre.org/techniques/T1110/ — Reference for the adversarial technique mapped to this vulnerability.
4. CWE-307 — Improper Restriction of Excessive Authentication Attempts: https://cwe.mitre.org/data/definitions/307.html — The weakness class that this vulnerability falls under.
5. RFC 6238 — TOTP: Time-Based One-Time Password Algorithm: https://datatracker.ietf.org/doc/html/rfc6238 — The relevant standard for the TOTP mechanism that this vulnerability targets.

Threat Actor / Exploit-in-the-Wild Status: No known threat actor campaigns have been publicly attributed to CVE-2026-76213 as of this report. The CVE is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and there is no evidence of active exploitation in the wild. The lack of a public PoC or Nuclei template suggests that exploitation is not yet widespread; however, the vulnerability class is well-understood and the attack is straightforward to implement for any attacker who already has valid credentials. Organizations should treat this as a high-priority patching item given the ease of exploitation once a password is compromised. The EPSS (Exploit Prediction Scoring System) has not yet assigned a score to this CVE.