CVE-2026-78124: strongSwan Use-After-Free Vulnerability

CVE-2026-78124 Overview

CVE-2026-78124 is a memory leak vulnerability in strongSwan, an open-source IPsec-based VPN solution. Versions 5.0.2 through 6.0.7 fail to release memory after its effective lifetime during PKCS#7 certificate enumeration in the openssl plugin. A remote attacker can trigger repeated allocations that are never freed, gradually consuming process memory. The flaw is tracked under [CWE-401: Missing Release of Memory after Effective Lifetime].

Critical Impact
Sustained exploitation can degrade strongSwan daemon performance and lead to resource exhaustion on gateways that process attacker-supplied PKCS#7 certificates.

Affected Products

strongSwan 5.0.2 through 6.0.7
Deployments using the openssl plugin for PKCS#7 handling
IPsec VPN gateways relying on affected strongSwan builds

Discovery Timeline

2026-09-07 - strongSwan project publishes vulnerability advisory
2026-09-11 - CVE-2026-78124 published to NVD
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2026-78124

Vulnerability Analysis

The vulnerability resides in the openssl plugin's PKCS#7 certificate enumeration path. When strongSwan iterates over certificates contained in a PKCS#7 structure, allocated OpenSSL objects are not consistently released back to the heap. Each enumeration therefore leaves residual allocations tied to the strongSwan daemon process.

An unauthenticated remote peer can drive this code path by submitting crafted PKCS#7 payloads during IKE exchanges. Repeated submissions cause monotonic memory growth in charon or related daemons. Over time, the process consumes available memory and impacts VPN service availability.

The issue affects only the confidentiality dimension in scoring terms; however, the practical operational impact is service degradation on long-running IPsec gateways. High attack complexity reflects the specific conditions required to trigger the enumeration path against a vulnerable configuration.

Root Cause

The root cause is a missing free operation in the PKCS#7 certificate enumeration logic of the openssl plugin. OpenSSL objects allocated during iteration are not paired with the corresponding release calls when the enumerator finishes, matching the pattern described in [CWE-401].

Attack Vector

Exploitation occurs over the network against strongSwan endpoints that accept and parse PKCS#7 certificate content from remote peers. No authentication or user interaction is required. The attacker repeatedly submits PKCS#7 material to grow the leaked allocation footprint in the target daemon.

No verified proof-of-concept code has been published. Refer to the strongSwan vulnerability advisory for authoritative technical detail.

Detection Methods for CVE-2026-78124

Indicators of Compromise

Steady, unexplained growth in resident set size (RSS) of the charon or strongSwan daemon process over hours or days
Elevated volumes of inbound IKE messages containing PKCS#7 certificate payloads from unfamiliar peers
strongSwan daemon restarts, OOM-killer events, or IPsec service interruptions on gateways running affected versions

Detection Strategies

Inventory strongSwan installations and flag any version in the range 5.0.2 through 6.0.7 that loads the openssl plugin
Baseline normal memory consumption of IPsec daemons and alert on deviations that lack a corresponding session count increase
Correlate IKE/IPsec traffic spikes with process memory metrics to identify certificate enumeration abuse

Monitoring Recommendations

Ship strongSwan logs and host process metrics to a centralized analytics platform for longitudinal review
Track charon uptime and memory trend lines per VPN concentrator
Alert on repeated PKCS#7 parsing errors or enumerator invocations from a single remote source

How to Mitigate CVE-2026-78124

Immediate Actions Required

Upgrade strongSwan to release 6.1.0 or later, which addresses the leak per the GitHub release notes
Restart the strongSwan daemon after patching to release accumulated memory
Restrict IKE exposure to known peer networks where feasible while patching is scheduled

Patch Information

The strongSwan project fixed CVE-2026-78124 in version 6.1.0. Distribution maintainers may backport the fix into prior branches; verify the exact package version supplied by your Linux distribution before considering a system remediated. See the strongSwan advisory for authoritative fix guidance.

Workarounds

Where certificate-based authentication using PKCS#7 is not required, disable or avoid loading the openssl plugin path that performs PKCS#7 enumeration
Enforce peer allow-lists at the firewall to limit which sources can initiate IKE exchanges against the gateway
Schedule periodic daemon restarts on unpatched gateways to reclaim leaked memory until upgrade is complete

bash

# Verify installed strongSwan version
ipsec --version
strongswan version

# Example package upgrade (Debian/Ubuntu)
sudo apt update
sudo apt install --only-upgrade strongswan strongswan-libcharon

# Restart the IPsec daemon to release accumulated memory
sudo systemctl restart strongswan