CVE-2024-8096: Haxx Curl Information Disclosure Vulnerability

CVE-2024-8096 Overview

CVE-2024-8096 is an Improper Certificate Validation vulnerability in curl, the widely-used open-source command-line tool and library for transferring data with URLs. When curl is configured to use the Certificate Status Request TLS extension (commonly known as OCSP stapling) to verify server certificate validity, it fails to properly detect certain OCSP response errors. Specifically, if the OCSP response returns an error status other than 'revoked' (such as 'unauthorized'), curl incorrectly treats the certificate as valid rather than rejecting it.

This vulnerability affects the fundamental trust model of TLS connections by allowing potentially problematic certificates to be accepted when OCSP stapling verification should have flagged issues with the certificate's status.

Critical Impact

Applications using curl with OCSP stapling enabled may establish TLS connections with servers presenting certificates that have unverifiable or problematic OCSP status, potentially allowing man-in-the-middle attacks or connections to unauthorized servers.

Affected Products

• Haxx curl (versions prior to the security fix)
• Debian Linux 11.0
• NetApp Active IQ Unified Manager (VMware vSphere)
• NetApp ONTAP Select Deploy Administration Utility
• NetApp ONTAP Tools 10 (VMware vSphere)
• NetApp Bootstrap OS
• NetApp HCI Compute Node
• NetApp H300S, H410S, H500S, H700S (hardware and firmware)

Discovery Timeline

• September 11, 2024 - CVE-2024-8096 published to NVD
• July 30, 2025 - Last updated in NVD database

Technical Details for CVE-2024-8096

Vulnerability Analysis

This vulnerability stems from improper certificate validation (CWE-295) in curl's implementation of OCSP stapling verification. OCSP stapling is a mechanism where the server presents a timestamped OCSP response during the TLS handshake, eliminating the need for the client to contact the OCSP responder directly.

The flaw exists in how curl processes the OCSP response status codes. When the OCSP responder returns an error condition, curl's validation logic only explicitly checks for the 'revoked' status. Other error statuses such as 'unauthorized', 'tryLater', 'sigRequired', or 'internalError' are not properly handled, causing curl to treat these responses as if the certificate status check passed successfully.

This creates a security gap where certificates with unverifiable OCSP status are incorrectly accepted, undermining the purpose of OCSP stapling as a certificate revocation checking mechanism.

Root Cause

The root cause is incomplete error handling in curl's OCSP response validation code. The implementation fails to treat all non-success OCSP response statuses as certificate validation failures. Instead, it only specifically rejects certificates when the OCSP status is explicitly 'revoked', while other error conditions fall through as acceptable.

This logic error means that when an OCSP responder cannot or will not provide a definitive status for a certificate (returning statuses like 'unauthorized'), curl proceeds as if the certificate passed validation, rather than applying a fail-secure approach.

Attack Vector

The vulnerability can be exploited through a network-based attack where an attacker controls or influences the TLS handshake process. The attack requires the target application to use curl with OCSP stapling enabled (--cert-status option or equivalent libcurl configuration).

An attacker could potentially leverage this vulnerability by presenting a certificate with an OCSP stapled response containing a non-'revoked' error status. The target curl client would then incorrectly accept the connection, even though the certificate's validity could not be properly verified through OCSP.

This could facilitate man-in-the-middle attacks or allow connections to servers with certificates that should have been rejected due to OCSP verification failures.

Detection Methods for CVE-2024-8096

Indicators of Compromise

• Unexpected TLS connections established with servers where OCSP stapling returned non-'good' status codes
• Certificate status verification warnings or errors in system logs that were not followed by connection termination
• Network traffic showing TLS connections proceeding despite OCSP responses with error status values
• Applications using curl with --cert-status flag connecting to potentially untrusted endpoints

Detection Strategies

• Audit curl and libcurl versions across all systems and applications to identify vulnerable installations
• Review application configurations to determine which services are using curl with OCSP stapling enabled
• Monitor TLS connection logs for certificates with unusual or error OCSP status responses
• Implement network monitoring to detect connections established despite OCSP verification anomalies

Monitoring Recommendations

• Enable verbose logging for curl operations to capture detailed TLS handshake and certificate verification information
• Deploy network inspection tools to analyze OCSP response status codes in stapled TLS connections
• Create alerts for any instances where OCSP responses contain status values other than 'good' or 'revoked'
• Track curl version deployments across your infrastructure using software inventory management

How to Mitigate CVE-2024-8096

Immediate Actions Required

• Update curl to the latest patched version that addresses CVE-2024-8096
• Review all applications and scripts using curl with OCSP stapling (--cert-status) and assess the security impact
• Consider temporarily disabling OCSP stapling verification if updates cannot be immediately applied
• Implement additional certificate validation mechanisms such as Certificate Transparency log verification

Patch Information

The curl project has released a security patch to address this vulnerability. Organizations should update to the latest version of curl that includes the fix. Detailed patch information is available in the cURL CVE-2024-8096 Documentation.

For Debian systems, refer to the Debian LTS Announcement #00008 for distribution-specific update instructions.

NetApp customers should consult the NetApp Security Advisory NTAP-20241011-0005 for guidance on affected NetApp products and remediation steps.

Workarounds

• Disable OCSP stapling verification by removing the --cert-status option from curl commands until patching is complete
• Implement additional certificate validation at the application layer using certificate pinning
• Use certificate transparency validation as a complementary verification mechanism
• Deploy network-level TLS inspection that independently validates OCSP status

# Configuration example
# Verify curl version to ensure it is patched
curl --version

# Temporarily disable OCSP stapling verification
# Instead of: curl --cert-status https://example.com
# Use: curl https://example.com

# Update curl on Debian-based systems
sudo apt-get update && sudo apt-get upgrade curl

# Update curl on RHEL/CentOS systems
sudo yum update curl