CVE-2026-0516

Executive Summary

CVE-2026-0516 is a medium-severity HTTP header injection vulnerability — specifically an improper neutralization of HTTP Headers for Scripting Syntax (CWE-644) — affecting SonicWall SonicOS, the operating system powering SonicWall next-generation firewalls. A remote, unauthenticated attacker can manipulate the HTTP Host header during management-plane session establishment, redirecting firewall administrators to attacker-controlled web domains. This can lead to credential harvesting via phishing, session token theft, or users unknowingly executing malicious JavaScript in the context of the legitimate management interface. With a CVSS score of 6.5 (Medium), the vulnerability requires no authentication or user interaction to trigger the redirect, though successful impact depends on an administrator following the redirect. The vulnerability is currently unpatched (patch confidence 0/4), and no public exploit code or CISA KEV listing exists as of this report, though the medium EPSS score (0.00205) suggests limited near-term exploitation likelihood.

Technical Analysis

The vulnerability resides in SonicOS's HTTP request handling component responsible for parsing and validating the Host header on management-plane interfaces (e.g., HTTPS management on ports 443, 8443, or 4444, depending on model configuration). The root cause is an improper neutralization of HTTP Headers for Scripting Syntax (CWE-644). This class of flaw occurs when the application reflects or uses user-supplied HTTP header values (in this case, Host) within dynamically constructed URLs, HTML content, or redirect responses without proper sanitization, encoding, or validation.

Attack Surface:

The reachable attack surface includes any HTTP(S) management interface exposed on SonicWall firewalls — either directly from the internet (misconfigured deployments) or, more commonly, from the internal network and VPN zones. SonicOS management interfaces historically allow unauthenticated access to login pages and certain diagnostic endpoints. The vulnerable code path likely sits in the login redirect logic, session establishment handlers, or captive-portal-style redirect components that construct a Location header or client-side window.location assignment based on the incoming Host header value.

Mechanism (Inferred from Vulnerability Class):

1. An attacker sends an HTTP GET request to the SonicOS management interface with a modified Host header, for example: Host: malicious.example.com.
2. Servers that blindly trust the Host header when constructing redirect URLs — e.g., after a failed login, session timeout, or during initial page load for captive-portal-like flows — will emit a Location: https://malicious.example.com/login header, or embed the attacker-controlled domain in the HTML body via JavaScript (e.g., window.location = "https://" + document.location.host + "/login").
3. The firewall administrator's browser follows the redirect to the attacker's domain, which may host a pixel-perfect clone of the SonicWall login page, capturing credentials, MFA tokens, or session cookies.
4. Because the malicious domain is served over HTTPS (the attacker can obtain a valid certificate), browser warnings are suppressed, and the user has no visible indication of the attack.

Code-Level Insight (Hypothetical but Consistent):

Typical vulnerable pseudocode:

def handle_login_redirect(request):
    host = request.headers.get("Host", "unknown")
    # VULNERABLE: no validation on host value
    return redirect(f"https://{host}/auth/login")

The Host header is attacker-controlled in HTTP/1.1 and is only validly enforced when the server has explicit hostname allow-listing or virtual-host configuration that rejects unknown Host values. SonicOS, by default, accepts any Host value for the management IP address, creating the injection point.

CWE-644 Specifics:

CWE-644 describes failures to encode or sanitize HTTP header values before reflecting them in scripting contexts (HTML, JavaScript). The impact includes stored XSS if the header is persisted, or reflective XSS/URL poisoning if used transiently. For this CVE, the scripting syntax neutralization failure manifests as a URL-based redirect (URL poising), which is a functional precursor to both XSS and credential phishing.

Exploitation Scenarios

Scenario A — Credential Phishing via Host Header Redirect (External Attacker)

1. Reconnaissance: The attacker scans the IPv4 space for SonicWall management interfaces using Shodan dorks (e.g., http.title:"SonicWall", product:"SonicWall"). They identify targets where the management port (443, 8443, 44444) is exposed to the internet.
2. Weaponization: The attacker registers a domain (e.g., sonicwall-update.example) and creates a TLS certificate for it. They clone the SonicWall login page, including all static assets (CSS, logos, JS scripts) downloaded from the legitimate interface.
3. Delivery / Trigger: Using a tool like curl or Burp Suite, the attacker crafts the following request:

GET / HTTP/1.1
Host: sonicwall-update.example
Accept: text/html

The SonicOS server, vulnerable to the Host header manipulation, processes the login page request and emits an HTTP 302 redirect:

HTTP/1.1 302 Found
Location: https://sonicwall-update.example/auth/login

4. Social Engineering: The attacker lures the firewall administrator (whose IP they identified via Shodan or who is on the same network segment) to the URL — e.g., via a crafted email link pointing to https://[firewall-ip]/ which triggers the redirect silently, or via a link directly to https://[firewall-ip]/ that the browser follows and lands on the malicious clone.

Scenario B — Session Hijacking Through Cookie Theft (Internal Attacker)

1. An authenticated administrator is actively using the SonicOS management UI.
2. The attacker (e.g., a malicious insider or an attacker who has already completed lateral movement) on the same LAN sends a specially crafted HTTP request to the management interface with Host: evil.com. This can be done by crafting a direct socket connection or using tools like nc or python requests.
3. If the server reflects the Host header into a Set-Cookie domain attribute or into a client-side script that sets document.cookie with a domain-scoped cookie, the attacker can capture the admin's session token when the browser executes the poisoned script.
4. The attacker then impersonates the administrator session and modifies firewall rules, exfiltrates logs, or disables security features.

Scenario C — XSS to RCE (Chained)

1. The attacker exploits the header reflection to inject a </script><script>alert(document.cookie)</script> payload in the Host header.
2. The server constructs a JavaScript snippet: var host = "injected</script><script>…</script>"; which, when parsed, executes the attacker's JavaScript in the admin's browser context.
3. The script can then make authenticated API calls to the firewall's management API (e.g., adding a new VPN user, disabling the firewall, exfiltrating route tables, or uploading a malicious firmware package if the API supports it), achieving near-total control of the device.

Post-Exploitation Impact: Whether phishing or XSS is achieved, the attacker gains valid admin credentials or a session token. They can then fully configure the firewall: pivot into the internal network, drop logs, exfiltrate sensitive traffic, or install persistent backdoors via firmware tampering.

Impact Assessment

CVSS Sub-Score Analysis (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N):

• Attack Vector: Network (AV:N) — The vulnerability is exploitable remotely over the network. No adjacent-network access required.
• Attack Complexity: Low (AC:L) — No special conditions or race conditions. The attacker simply crafts a malicious HTTP request.
• Privileges Required: None (PR:N) — No authentication is needed to reach the vulnerable handler.
• User Interaction: None (UI:N) — The initial exploit (redirect) requires no user action. However, full credential compromise requires the admin to click through the redirect, but that is not part of the CVSS user-interaction metric (which measures the exploit itself).
• Scope: Unchanged (S:U) — The vulnerability impacts only the management plane, not other components.
• Confidentiality Impact: Low (C:L) — Limited data exposure; the attacker may capture admin credentials or session tokens, which can then be used to access configuration data.
• Integrity Impact: Low (I:L) — Potential for configuration manipulation if session hijacking succeeds.
• Availability Impact: None (A:N) — The flaw does not cause denial of service.

Business Impact:

Blast Radius: Perimeter firewalls are high-impact targets — they sit at the network edge, control all ingress/egress traffic, and often contain VPN services, routing rules, and security policies. A single compromised SonicWall device can expose an entire internal network to lateral movement.

Detection Guidance

Sigma Rule

title: SonicWall SonicOS Host Header Injection Attempt (CVE-2026-0516)
id: 6f3e7a8b-2c4d-4e5f-8a9b-0c1d2e3f4a5b
status: experimental
description: Detects HTTP requests to SonicWall management interfaces with anomalous Host headers that differ from the expected management hostname or IP.
author: valtersit.com Threat Intel
date: 2026/06/15
logsource:
  category: webserver
  product: sonicos
detection:
  selection:
    http.response.code:
      - 301
      - 302
    http.url|contains: 
      - "/auth/"
      - "/login"
      - "/sslvpn"
    http.host|contains:
      - "%"
      - "script"
      - "<"
      - ">"
      - "javascript:"
  filter:
    http.host|startswith:
      - "192.168."
      - "10."
      - "172."
  condition: selection and not filter
level: medium
falsepositives:
  - Legitimate multi-tenant or virtual-host configurations using non-IP hostnames
tags:
  - attack.t1190
  - cve.2026.0516
  - cwe.644

YARA Rule

rule SonicWall_HeaderInjection_CVE2026_0516
{
    meta:
        author = "valtersit.com Threat Intel"
        description = "Detects payloads used to exploit Host header injection in SonicWall SonicOS"
        cve = "CVE-2026-0516"
        date = "2026-06-15"
        severity = "medium"
    strings:
        $a = /Host:\s*[^\r\n]*(script|href|%0d|%0a|<|>)/ nocase
        $b = "Location: http"
        $c = "window.location"
        $d = "document.location.host"
        $e = /Host:\s*(?!192\.168\.|10\.|172\.).*[a-z]{2,}[0-9]*\.(com|net|xyz|io|info|biz)/ nocase
    condition:
        any of them
}

Suricata IDS Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"SonicWall CVE-2026-0516 Host Header Injection Attempt"; flow:to_server,established; content:"Host:"; http_header; nocase; content:"script|3b|"; http_header; nocase; sid:20260516; rev:1; metadata:cve CVE-2026-0516; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-0516;)

Note: This Suricata rule detects Host header values containing script injection patterns. Additional rule variants could match on %0d%0a (CRLF) injection sequences or suspicious domain TLDs in the Host header.

Elastic Detection

sequence by host.name, source.ip with maxspan=5s
  [http where process.name == "sonicos" and event.action == "request"]
  [http where event.action == "response" and http.response.status_code == 302 and
   http.response.headers.locations == "https://*" and not http.url is null and
   not http.url contains "sonicwall.com"]

Splunk SPL Query

index=web sourcetype=sonicos:access
| where event.category=="http"
| search http.response.status_code=302
| regex http.request.host="(?i)(script|<|>|%0d|%0a|javascript)"
| stats count by src_ip, dest_ip, http.request.host, http.response.header.location
| sort - count

Wazuh OSSEC Rule

<group name="sonicos,">
  <rule id="100516" level="10">
    <if_sid>100001</if_sid>
    <match>Host:</match>
    <regex>Host:.*(script|&lt;|&gt;|%0d|%0a|javascript)</regex>
    <description>SonicWall Host Header Injection Attempt (CVE-2026-0516) detected.</description>
    <group>attack.t1190,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 (UNPATCHED) — no patch evidence from any tracked source as of 2026-06-15.

No vendor fix, patched version, or official workaround has been published by SonicWall or any third-party source. This does not guarantee a patch will never be released; it means none is currently identifiable across NVD, vendor advisories, or OSV trackers.

1) Immediate Mitigations (Compensating Controls)

2) Patch/Upgrade Steps

• Immediately check SonicWall’s official security advisory page (and subscribe to SonicWall PSIRT notifications) for any firmware release addressing CVE-2026-0516.
• When a patched firmware (e.g., SonicOS 7.x.y-z) is released, follow the standard upgrade path:
  1. Download the new firmware from SonicWall’s official portal (mysonicwall.com).
  2. Read the release notes to confirm CVE-2026-0516 is fixed.
  3. Schedule a maintenance window; back up current configuration.
  4. Upload and apply the firmware; reboot the device.
  5. Verify management interface availability and re-apply any configuration changes post-upgrade.
• Until a patch is available, no version upgrade will resolve this flaw.

3) Long-Term Hardening

• Move away from direct device management: Implement centralized management via SonicWall GMS (Global Management System) or a cloud-based orchestration platform that proxies management sessions and enforces strict host validation.
• Zero Trust Networking (ZTN): Ensure that no management interface is directly internet-facing. All admin access should funnel through a zero-trust access broker requiring continuous authentication/authorization.
• Security baselines: Develop a baseline configuration for all SonicWall deployments that includes: management VLAN isolation, SNMP disabled, HTTP management disabled (HTTPS-only), and default admin password rotation.
• Periodic security reviews: Include firewall management interfaces in quarterly penetration tests and red-team exercises.
• Threat intel subscription: Subscribe to SonicWall’s PSIRT bulletin and CISA KEV updates to receive immediate alerts when a patch is published.

References

1. NVD (National Vulnerability Database): https://nvd.nist.gov/vuln/detail/CVE-2026-0516 — Official CVE description, CVSS score, and CWE classification.
2. MITRE ATT&CK: https://attack.mitre.org/techniques/T1190/ — Exploit Public-Facing Application technique (mapped to this vulnerability).
3. SonicWall PSIRT (Pending): https://www.sonicwall.com/support/product-security/ — Vendor security advisory page; check for future patches concerning CVE-2026-0516.
4. CISA Known Exploited Vulnerabilities (KEV) Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — CVE-2026-0516 is NOT listed as of 2026-06-15, indicating no confirmed in-the-wild exploitation.
5. CWE-644 — Improper Neutralization of HTTP Headers for Scripting Syntax: https://cwe.mitre.org/data/definitions/644.html — Detailed CWE description and related weakness taxonomy.

Known Threat Actor Campaigns / Exploitation Evidence: As of this report date, no public exploit code, PoC, or confirmed in-the-wild exploitation has been observed. The EPSS score (0.00205, 10.6th percentile) indicates a low probability of exploitation in the near term. However, Host header injection and the associated phishing chain of vulnerabilities remain a common attack vector for perimeter devices; this CVE should be monitored closely, especially as SonicWall devices are prevalent in enterprise environments.