External risk intelligence

cURL FTP-Kerberos Double-Free Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2019-5481

This vulnerability resides in the curl library's FTP-kerberos code. While curl is a ubiquitous component used in countless applications, services, and embedded systems—some of which may be internet-facing—the library itself is a foundational building block rather than an end-user service. Its reachability depends entirely on how the specific host application utilizes the library to handle network traffic.

Haxx Curl

7.52.0 to 7.65.32930313.44.04.14.24.38.38.412.3.312.4.05.7.0 to 5.7.288.0.0 to 8.0.1820.09.010.015.015.1

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A double-free vulnerability exists in the FTP-kerberos code of the widely used cURL library, potentially affecting numerous applications and systems. This type of issue can lead to unpredictable program behavior and security risks. The main concern is confirming relevance and exposure within our environment.

An internal code flaw affects FTP file transfers.
It could impact the integrity of applications using this code.
Confirm if our systems use this vulnerable library component.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted network requests to a system using a vulnerable version of the cURL library. This could occur if the system makes outbound connections, such as when downloading files or interacting with remote services. The vulnerability in the FTP-kerberos code could then lead to critical compromise of the affected system.

Network access required.
Triggered by specific FTP-kerberos requests.
Enables critical system compromise.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in the FTP-kerberos code of cURL could allow a malicious FTP server to cause a double-free error. This error may lead to memory corruption when transferring data, potentially causing the application to crash.

Data corruption or application crash.
Malicious FTP server interaction.
Denial of service.

Operational Fix

Recommended remediation, mitigation, and detection steps

The `curl` library's FTP-kerberos component is affected by this vulnerability. Responsibility for addressing this issue likely falls to application owners who integrate `curl` into their software, platform teams managing shared libraries, and potentially vendor management teams if `curl` is part of a third-party solution. The immediate first step is to inventory systems using affected `curl` versions, assess their exposure and business criticality, and then coordinate remediation with accountable owners.

Application and platform teams own remediation.
Verify `curl` usage and asset exposure.
Plan and execute updates based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is cURL and why is it used?

cURL is a ubiquitous, foundational library and command-line tool used for transferring data across networks. Developers integrate it into countless applications, operating systems, and embedded firmware to handle protocol communications. Because it powers so much infrastructure, it is a common building block for network connectivity in both enterprise software and specialized device management tools.

What does this CVE-2019-5481 vulnerability mean?

This vulnerability is classified as a double-free (CWE-415), a specific type of memory management flaw. It occurs when a program attempts to release the same memory space twice. In this case, the weakness exists within the FTP-kerberos code. This error can corrupt memory, potentially leading to application crashes or unpredictable behavior when processing FTP traffic.

How is this cURL vulnerability triggered?

An attacker triggers this flaw by interacting with a system using a vulnerable version of cURL through the FTP-kerberos protocol. The vulnerability is typically exploited when a system acting as an FTP client connects to a malicious server that sends specially crafted responses. Normal, non-FTP, or non-kerberos network traffic will not trigger this specific memory error.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal notes that while cURL is common, risk depends on how your specific applications use it. Because cURL is a library rather than a standalone service, you must determine if your software uses the affected FTP-kerberos components and if those components handle untrusted network traffic. Reachability varies based on your unique application architecture.

What are the first steps to address CVE-2019-5481?

Begin by auditing your environment to inventory systems and applications running the vulnerable cURL versions. Because this is a library-level issue, coordinate with your platform and application teams to identify where cURL is embedded. Once identified, prioritize patching based on the business criticality of the affected systems and their exposure to network connections.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.