CVE-2019-1579

CVE-2019-1579: Format String Vulnerability in Palo Alto Networks PAN-OS GlobalProtect

AI-generated analysis based on the vulnerability data on this page.

Summary

CVE-2019-1579 is an unauthenticated remote code execution vulnerability in Palo Alto Networks PAN-OS. The flaw resides in the GlobalProtect Portal and GlobalProtect Gateway interfaces, where a format string bug (CWE-134) allows an attacker to execute arbitrary code without prior authentication. This vulnerability has been actively exploited in the wild and is listed in both the CISA Known Exploited Vulnerabilities catalog and the EU Vulnerability Database.

Background

Palo Alto Networks PAN-OS powers the company's next-generation firewalls. The GlobalProtect feature provides SSL VPN connectivity for remote users through both a portal (for client provisioning) and gateway (for VPN tunnel termination) interface. In mid-2019, researchers from DEVCORE identified a critical format string vulnerability in these interfaces that could be triggered by sending a specially crafted request to an exposed GlobalProtect endpoint. The vulnerability gained significant attention after it was disclosed that it had been exploited in targeted attacks.

Root Cause

The vulnerability is classified as CWE-134: Use of Externally-Controlled Format String. In affected versions of PAN-OS, user-supplied input was passed directly to a format function (such as sprintf or equivalent) without proper sanitization. When an attacker can control the format string specifier, they can read from or write to arbitrary memory locations. This primitive enables full remote code execution because the attacker can overwrite function pointers, return addresses, or other critical memory structures to hijack control flow. The lack of input validation on the GlobalProtect HTTP interface made this exploitable without any authentication credentials.

Impact

The vulnerability is rated HIGH severity with a CVSS v3 score of 8.1 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H). The impact scores reflect the severe consequences:

• Confidentiality Impact: HIGH — An attacker can access sensitive data stored on the firewall or within the protected network.
• Integrity Impact: HIGH — The attacker can modify system configurations, implant backdoors, or alter traffic policies.
• Availability Impact: HIGH — The attacker can crash the device or disrupt VPN services.

The CVSS v2 score is 6.8 (AV:N/AC:M/Au:N/C:P/I:P/A:P), also indicating significant risk. Despite the "High" attack complexity in CVSS v3, public exploitation has been confirmed, meaning reliable exploit methods exist and have been used by threat actors.

Exploitation Walkthrough

Ethics Notice: This section describes the vulnerability mechanism from a defensive perspective. No weaponized exploit code is provided. Understanding the attack path is essential for detection, mitigation, and verification of patches.

The exploitation chain generally follows these stages:

1. Reconnaissance: The attacker identifies a PAN-OS device with the GlobalProtect Portal or Gateway interface exposed to the internet, typically on TCP port 443.
2. Format String Injection: The attacker sends a crafted HTTP request containing format string specifiers (such as %n, %s, or %x) to a vulnerable endpoint in the GlobalProtect handler.
3. Memory Corruption: The unsanitized format string is processed by a logging or error-handling routine, causing memory reads or writes at attacker-controlled addresses.
4. Code Execution: By carefully crafting the format string and using repeated requests, the attacker achieves arbitrary code execution in the context of the web server process, which runs with elevated privileges on the firewall.

Because the flaw is reachable pre-authentication, no valid VPN credentials or session tokens are required. The attacker only needs network reachability to the GlobalProtect interface.

Affected and Patched Versions

According to Palo Alto Networks, the following PAN-OS versions are affected:

• PAN-OS 7.1.18 and earlier
• PAN-OS 8.0.11-h1 and earlier
• PAN-OS 8.1.2 and earlier

The vulnerability only manifests when the GlobalProtect Portal or GlobalProtect Gateway interface is enabled. Devices without these features activated are not exposed to this attack vector. Organizations should upgrade to versions newer than the affected ranges; consult the official Palo Alto Networks security advisory for the exact fixed release numbers.

Remediation

1. Upgrade PAN-OS: Apply the latest security patches from Palo Alto Networks that supersede the affected version ranges. Prioritize any internet-facing GlobalProtect gateways.
2. Disable Unnecessary Interfaces: If GlobalProtect Portal or Gateway is not required, disable these interfaces to eliminate the attack surface entirely.
3. Network Segmentation: Restrict access to GlobalProtect management interfaces to trusted IP ranges using external firewalls or network ACLs. Do not expose the management plane or GlobalProtect interfaces directly to the internet unless absolutely necessary.
4. Compensating Controls: Deploy intrusion detection/prevention systems with signatures for known CVE-2019-1579 exploitation attempts. Monitor for anomalous HTTP requests containing format string characters directed at GlobalProtect endpoints.

Detection

Defenders can detect exploitation or post-exploitation activity through several methods:

• Network Traffic Analysis: Monitor for HTTP requests to GlobalProtect endpoints containing unusual format string patterns (%n, %s, %x, %p) in parameters or headers.
• Endpoint/Host Logs: Review PAN-OS system logs for crashes or restarts of the sslvpn or panagent processes, which may indicate failed or successful exploitation attempts.
• File Integrity Monitoring: After patching, verify that no unexpected files, cron jobs, or user accounts have been created on the firewall.
• Threat Intelligence: Correlate firewall IP addresses against threat intelligence feeds for known exploitation campaigns targeting PAN-OS GlobalProtect.

Assessment

CVE-2019-1579 is not merely a theoretical risk. With an EPSS score of 0.39317 (approximately 39.3% probability of exploitation in the wild), it sits in the 98th percentile of tracked vulnerabilities, indicating exceptionally high real-world exploit likelihood. Its inclusion in the CISA KEV catalog (added 2022-01-10) and the EU Exploited Vulner Database confirms active, in-the-wild exploitation.

The combination of pre-authentication remote code execution, a high EPSS score, and confirmed ransomware affiliate usage makes this vulnerability a critical priority for remediation. Two key lessons emerge: first, user input must never be passed unsanitized to format functions; second, VPN concentrators and remote access solutions remain high-value targets that demand rigorous hardening and rapid patch cycles.

References

• https://security.paloaltonetworks.com/CVE-2019-1579
• https://devco.re/blog/2019/07/17/attacking-ssl-vpn-part-1-PreAuth-RCE-on-Palo-Alto-GlobalProtect-with-Uber-as-case-study/
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-1579
• http://www.securityfocus.com/bid/109310
• https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2019-0010