CVE-2023-24034

Executive Summary

CVE-2023-24034 is an open redirect vulnerability in the twilio_ajax_handler.php component of Nagios XI prior to version 5.9.3. An attacker can craft a link that forces a victim to visit a malicious site by abusing insufficient validation of redirect targets. Because exploitation requires user interaction and only affects the integrity of a redirect destination, the CVSS base score is low (3.1), but the flaw is a useful component in phishing and credential-harvesting chains targeting Nagios administrators.

Technical Analysis

The NVD description states: "An issue was discovered in twilio_ajax_handler.php in Nagios XI before 5.9.3. An attacker can force a user to visit a malicious site by using an open redirect vulnerability." This maps to CWE-601 (URL Redirection to Untrusted Site, commonly "Open Redirect").

Open redirect vulnerabilities arise when an application accepts a user-supplied parameter that controls a redirect destination and fails to validate or allowlist it before issuing an HTTP 3xx response or a client-side navigation. In this case, the affected surface is twilio_ajax_handler.php, one of the AJAX handler scripts shipped with Nagios XI. Based solely on the description provided, the handler accepts a redirect target that is not constrained to same-origin or an approved destination list, allowing an attacker to substitute an arbitrary external URL.

Key technical characteristics derivable from the provided data:

• Attack vector: Network (AV:N). The handler is reachable over HTTP/HTTPS as part of the Nagios XI web interface.
• Attack complexity: High (AC:H). The vector implies conditions beyond the attacker's direct control are needed for a reliable exploit — consistent with an open redirect that depends on victim behavior and possibly on application state or authentication context of the handler.
• Privileges required: None (PR:N). The redirect can be initiated without authenticated access to the redirecting script itself (based on the CVSS vector).
• User interaction: Required (UI:R). The victim must click or be directed to the crafted URL.
• Scope: Unchanged (S:U). Impact is confined to the application/browser context.
• Confidentiality: None (C:N); Integrity: Low (I:L); Availability: None (A:N). No direct data compromise or denial of service — the impact is the redirection to attacker-controlled infrastructure.

No specific parameter names, exact redirect response codes, or validation logic are disclosed in the provided NVD description or CNA title. Any claim about a specific query-string parameter would be speculative and is therefore deliberately not made here.

Because the redirect initiates from a trusted Nagios XI host, it is well-suited for phishing: the initial URL appears legitimate (it points to the organization's own monitoring server), which can bypass naive URL-reputation filters and user suspicion and then hand the victim off to an attacker-controlled page.

Exploitation Scenarios

No public PoC or Nuclei template is available, and no exploit code has been observed. The attack chain below is inferred strictly from the vulnerability class (CWE-601) and the fact pattern in the NVD description. It does not assume specific parameter names beyond those established in the description.

1. Reconnaissance / target identification The attacker enumerates internet- or intranet-exposed Nagios XI instances (e.g., via Shodan/fingerprinting of the Nagios XI login interface). The goal is to identify hosts running a version prior to 5.9.3 and to confirm that twilio_ajax_handler.php is reachable.

2. Triggering the open redirect The attacker constructs a URL that points to the vulnerable twilio_ajax_handler.php endpoint on the victim organization's Nagios XI host and appends a redirect destination controlled by the attacker. The exact parameter name controlling the redirect is not disclosed in the available description, so no specific parameter is asserted here. The attacker delivers this link via email, chat, or a social-engineering message (consistent with T1204.001 — Malicious Link).

3. Payload / execution method When the victim clicks the link, the request reaches the trusted Nagios XI server, which responds by redirecting the victim's browser to the attacker-chosen site. At the vulnerability-class level, the "payload" is the attacker-supplied redirect target; execution depends entirely on the victim following the link (UI:R).

4. Post-exploitation impact Once redirected, the victim lands on attacker infrastructure — typically a credential-harvesting page styled to look like a Nagios, SSO, or corporate login, or a malware delivery page. The success of this phase depends on the attacker's secondary payload, not on the redirect itself. The redirect provides cover and trust transference; the direct CVE impact remains an integrity-only redirection (I:L).

Note: Any exploitation in the wild would require the victim to interact; the EPSS score (0.00385, ~32.2nd percentile) indicates low predicted exploitation activity, and the CVE is NOT listed in CISA KEV.

Impact Assessment

Business impact is primarily phishing enablement rather than direct compromise. Because the redirect originates from a trusted Nagios XI monitoring server — infrastructure frequently allowlisted and trusted by security and IT teams — users are more likely to click through, and URL-reputation tooling may fail to block the initial hop. Successful phishing can lead to credential theft for the Nagios XI console (which may itself expose infrastructure-wide monitoring data and configuration) or for corporate identity providers, escalating a low-CVSS bug into a higher-impact compromise.

Affected systems: any deployment of Nagios XI prior to 5.9.3 with the twilio_ajax_handler.php handler exposed to a network the attacker can reach (directly or via the victim's browser).

Blast radius is bounded by the CVSS subscores:

• AV:N — remotely reachable.
• AC:H — non-trivial conditions reduce reliability.
• PR:N — no prior authentication needed to reach the handler.
• UI:R — requires the victim to click.
• S:U, C:N, I:L, A:N — no scope change; no confidentiality or availability impact; only low integrity impact (the redirect destination).

Overall the direct technical severity is low (3.1), but the strategic value in social-engineering chains can be materially higher than the numeric score suggests.

Detection Guidance

Sigma Rule

Detects requests that target the vulnerable handler with an external (off-domain) redirect destination parameter — a pattern consistent with open-redirect abuse against Nagios XI.

title: Nagios XI Open Redirect Abuse via twilio_ajax_handler.php (CVE-2023-24034)
id: 3f6a1c9e-2403-4b7b-9b7a-24034nagiosxi
status: experimental
description: Detects HTTP requests to Nagios XI twilio_ajax_handler.php containing off-domain redirect targets, indicative of CVE-2023-24034 open redirect abuse.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2023-24034
author: valtersit.com
date: 2025-01-01
logsource:
  category: webserver
  product: apache
detection:
  selection_endpoint:
    cs-uri-stem|endswith:
      - '/twilio_ajax_handler.php'
  selection_redirect_param:
    cs-uri-query|contains:
      - 'redirect='
      - 'return='
      - 'url='
      - 'next='
      - 'callback='
  filter_external:
    cs-uri-query|contains:
      - 'redirect=//'
      - 'return=//'
      - 'url=http://'
      - 'url=https://'
      - 'next=http'
      - 'callback=http'
  condition: selection_endpoint and (selection_redirect_param) and filter_external
falsepositives:
  - Legitimate internal redirects if linking to fully qualified internal hostnames.
level: medium
tags:
  - attack.t1204.001
  - cve.2023.24034

YARA Rule

Detection for webserver request/access logs referencing the vulnerable handler with an off-domain redirect indicator. This rule targets log artifacts rather than binaries, since no binary-level indicator is provided.

rule CVE_2023_24034_NagiosXI_OpenRedirect_Log
{
    meta:
        author = "valtersit.com"
        description = "Detects access-log/HTTP request lines referencing Nagios XI twilio_ajax_handler.php with off-domain redirect indicators (CVE-2023-24034)"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-24034"
        date = "2025-01-01"
        severity = "low"

    strings:
        $ep = "twilio_ajax_handler.php" ascii nocase
        $p1 = "redirect=" ascii nocase
        $p2 = "return=" ascii nocase
        $p3 = "url=" ascii nocase
        $p4 = "next=" ascii nocase
        $ext1 = "http://" ascii nocase
        $ext2 = "https://" ascii nocase
        $ext3 = "//" ascii

    condition:
        $ep and any of ($p*) and any of ($ext*)
}

Suricata IDS Rule

Alerts on HTTP requests to the vulnerable Nagios XI handler carrying an off-domain redirect target.

alert http any any -> any any (msg:"CVE-2023-24034 Nagios XI twilio_ajax_handler.php Open Redirect Attempt"; flow:to_server,established; http.uri; content:"twilio_ajax_handler.php"; nocase; http.uri; pcre:"/(redirect|return|url|next|callback)=/i"; http.uri; pcre:"/(redirect|return|url|next|callback)=[^&]*(https?:)?\/\//i"; reference:cve,2023-24034; reference:url,nvd.nist.gov/vuln/detail/CVE-2023-24034; classtype:attempted-recon; sid:202324034; rev:1;)

Elastic Detection

EQL rule matching web access events that hit the vulnerable endpoint with an off-domain redirect value.

network where
  event.category == "network" and
  (http.request.method == "GET" or http.request.method == "POST") and
  stringContains(http.request.path, "twilio_ajax_handler.php") and
  (
    stringContains(http.request.body, "redirect=") or
    stringContains(http.request.body, "return=") or
    stringContains(http.request.body, "url=") or
    stringContains(http.request.body, "next=") or
    stringContains(http.request.query, "redirect=") or
    stringContains(http.request.query, "return=") or
    stringContains(http.request.query, "url=") or
    stringContains(http.request.query, "next=")
  ) and
  (stringContains(http.request.body, "http://") or
   stringContains(http.request.body, "https://") or
   stringContains(http.request.query, "http://") or
   stringContains(http.request.query, "https://"))

Splunk SPL Query

Detects requests to the vulnerable handler with off-domain redirect indicators in access or proxy logs.

index=web OR index=proxy
| eval uri=coalesce(uri, url, cs_uri_stem, request)
| where like(uri, "%twilio_ajax_handler.php%")
| where match(uri, "(?i)(redirect|return|url|next|callback)=([^&]*)(https?:)?//")
| stats count min(_time) as first_seen max(_time) as last_seen values(uri) as uris by src_ip, dest_host
| sort - count

Wazuh OSSEC Rule

Custom Wazuh rule matching web access-log lines that target the vulnerable handler with an off-domain redirect.

<group name="nagios_xi,web,">
  <rule id="100340" level="6">
    <decoded_as>web-accesslog</decoded_as>
    <url>twilio_ajax_handler\.php</url>
    <regex type="pcre2">(?i)(redirect|return|url|next|callback)=([^&]*)(https?:)?//</regex>
    <description>CVE-2023-24034: Possible Nagios XI open redirect attempt against twilio_ajax_handler.php with off-domain target</description>
    <mitre>
      <id>T1204.001</id>
    </mitre>
    <group>cve_2023_24034,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix or workaround is recorded in the provided data; treat the environment as unpatched until the vendor advisory confirms a release.

1. Immediate mitigations

• Restrict network access to the Nagios XI web interface to trusted management networks and VPNs; do not expose it directly to the internet.
• Deploy URL filtering / Safe Links protections at the email and web gateway to detect redirects to unknown external domains.
• Enable user awareness controls for phishing that uses trusted internal hosts (e.g., your own monitoring server) as the initial hop.
• Monitor web access logs for requests to twilio_ajax_handler.php containing off-domain redirect parameters, using the detection rules above.
• Where supported, apply application-level input validation or a reverse-proxy rule to reject external destinations supplied to the handler (this is a compensating control, not a vendor patch).

2. Patch/upgrade steps

• Upgrade Nagios XI to version 5.9.3 or later, per the NVD description ("before 5.9.3").
• Verify the installed version from the Nagios XI UI and confirm the twilio_ajax_handler.php behavior no longer permits external redirect destinations.
• After upgrading, re-test the handler with a crafted external redirect target to confirm the fix.

3. Long-term hardening

• Maintain an asset inventory and patch-tracking process for Nagios XI and all internet-facing monitoring tools.
• Enforce allowlist-based redirect validation patterns in any in-house PHP/JS components.
• Keep Nagios XI behind authentication and network segmentation; treat monitoring consoles as high-value targets.
• Continuously track EPSS and vendor advisories; subscribe to Nagios security announcements.

References

• NVD — CVE-2023-24034: https://nvd.nist.gov/vuln/detail/CVE-2023-24034
• CWE-601 — URL Redirection to Untrusted Site ("Open Redirect"): https://cwe.mitre.org/data/definitions/601.html
• Nagios XI Security / product page (vendor): https://www.nagios.com/products/nagios-xi/
• FIRST EPSS — CVE-2023-24034 score lookup: https://api.first.org/data/v1/epss?cve=CVE-2023-24034
• CISA Known Exploited Vulnerabilities Catalog (CVE not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / in-the-wild note: No public PoC, Nuclei template, or exploit code is available. The CVE is NOT in CISA KEV, and EPSS (0.00385, ~32.2nd percentile) indicates low predicted exploitation. No threat actor campaign is associated with this CVE in the provided data.