CVE-2020-3259

CVE-2020-3259 is a high-severity vulnerability in Cisco Firepower Threat Defense with a CVSS 3.x base score of 7.5. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2024-02-15). The underlying weakness is classified as CWE-200.

Key facts

Description

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to retrieve memory contents on an affected device, which could lead to the disclosure of confidential information. The vulnerability is due to a buffer tracking issue when the software parses invalid URLs that are requested from the web services interface. An attacker could exploit this vulnerability by sending a crafted GET request to the web services interface. A successful exploit could allow the attacker to retrieve memory contents, which could lead to the disclosure of confidential information. Note: This vulnerability affects only specific AnyConnect and WebVPN configurations. For more information, see the Vulnerable Products section.

CVE-2020-3259: Cisco ASA/FTD Web Services Information Disclosure

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

Summary

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software allows an unauthenticated, remote attacker to read memory contents from an affected device. Successful exploitation leads to disclosure of confidential information. This vulnerability only impacts devices with specific AnyConnect and WebVPN configurations.

Background

Cisco ASA Software and Cisco FTD Software provide VPN and firewall capabilities for enterprise networks. The web services interface, used for AnyConnect and WebVPN sessions, handles URL parsing to serve remote-access portal pages. A buffer tracking flaw in this interface became a critical information-disclosure vector.

Root Cause

The vulnerability is caused by CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. The software fails to properly track buffer boundaries when parsing invalid URLs requested from the web services interface. This weakness allows an attacker to read memory beyond the intended buffer, resulting in disclosure of sensitive information such as session tokens, credentials, or configuration data.

Impact

The CVSS 3.1 score for this vulnerability is 7.5 (HIGH). The scoring metrics are:

  • Attack Vector (AV): Network
  • Attack Complexity (AC): Low
  • Privileges Required (PR): None
  • User Interaction (UI): None
  • Scope (S): Unchanged
  • Confidentiality (C): High
  • Integrity (I): None
  • Availability (A): None

Because the attack requires no authentication and no user interaction, the vulnerability is easily exploitable by any remote actor with network access to the affected interface.

Exploitation Walkthrough

An attacker can exploit this vulnerability by sending a crafted GET request to the web services interface with an invalid URL structure. The malformed request causes the URL parser to misread buffer boundaries, leaking adjacent memory contents back to the attacker in the response. This is a passive, defensive disclosure: the attacker cannot directly control what is leaked, but repeated requests may reveal fragments of sensitive data.

Ethics and safety note: This section is provided for defensive awareness only. Network defenders should use this knowledge to understand the attack surface and prioritize patching. The author does not endorse unauthorized testing on systems without explicit permission.

Affected and Patched Versions

Affected products:

  • Cisco Adaptive Security Appliance (ASA) Software
  • Cisco Firepower Threat Defense (FTD) Software

The vulnerability affects only specific AnyConnect and WebVPN configurations. For exact vulnerable version ranges and patch levels, consult the Cisco Security Advisory referenced below. The vendor released fixed software versions after disclosure.

Remediation

  1. Upgrade to the fixed software version provided by Cisco.
  2. Disable the web services interface if AnyConnect and WebVPN are not required.
  3. Apply compensating controls:
    • Restrict access to the web services interface using strict firewall rules and VPN segmentation.
    • Monitor the interface for anomalous GET requests with malformed or oversized URL parameters.
    • Enable logging and alert on repeated invalid URL access attempts from unexpected source IPs.
  4. Rotate any credentials or session material that may have been exposed if exploitation is suspected.

Detection

Defenders can detect potential exploitation by looking for:

  • Unusual GET requests to the web services interface containing non-standard or malformed URLs.
  • Repeated HTTP 200 or 500 responses from the web services interface with unusually large body sizes.
  • Network traffic anomalies targeting the AnyConnect or WebVPN portal from external, untrusted sources.

Assessment

With an EPSS score of 0.71789 and a KEV entry dated 2024-02-15, this vulnerability is a high-priority risk that is actively exploited in the wild. Organizations should treat patching as urgent, especially for internet-facing VPN concentrators. The key lessons from this case are: (1) buffer tracking in URL parsers is a recurring source of severe information disclosure, and (2) internet-accessible remote-access gateways must be kept on the shortest possible patch cycle because they are high-value targets.

References

Frequently asked questions

What is CVE-2020-3259?
A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to retrieve memory contents on an affected device, which could lead to the disclosure of confidential information. The vulnerability is due to a buffer tracking issue when the software parses invalid URLs that are requested from the web services interface. An attacker could exploit this vulnerability by sending a crafted GET request to the web services interface. A successful exploit could allow the attacker to retrieve memory contents, which could lead to the disclosure of confidential information. Note: This vulnerability affects only specific AnyConnect and WebVPN configurations. For more information, see the Vulnerable Products section.
How severe is CVE-2020-3259?
CVE-2020-3259 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2020-3259 being actively exploited?
Yes. CVE-2020-3259 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2024-02-15, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2020-3259?
CVE-2020-3259 primarily affects Cisco Firepower Threat Defense. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-3259?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2020-3259 have an EU (EUVD) identifier?
Yes. CVE-2020-3259 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2020-24530. It is also flagged as exploited in the EUVD (since 2024-02-15).
When was CVE-2020-3259 published?
CVE-2020-3259 was published on 2020-05-06 and last updated on 2026-06-17.

References

Affected products (2)

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