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Strongswan CVE-2026-25075

| EUVDEUVD-2026-14477 HIGH
Integer Underflow (CWE-191)
2026-03-23 VulnCheck GHSA-frr2-5qjr-h4hw
Denial Of Service Integer Overflow Strongswan
8.7
CVSS 4.0 · Vendor: VulnCheck
Temporal: 7.5
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Send crafted IKEv2 authentication packet
  2. Delivery
    Deliver malformed EAP-TTLS AVP data
  3. Exploit
    Trigger integer underflow in AVP parser
  4. Execution
    Cause excessive memory allocation
  5. Impact
    Crash charon IKE daemon

Vulnerability Assessment

Weakness
CWE
CWE-191
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Integer underflow checks
Exploitation Conditions

strongSwan versions 4.5.0 through 6.0.5 with EAP-TTLS authentication enabled during IKEv2 negotiation. Unauthenticated remote attacker sends crafted IKEv2 packets with malformed AVP length fields to crash the charon daemon. No victim interaction required.
Impact

This vulnerability presents a significant real-world denial-of-service risk. The CVSS 3.1 score of 7.5 (High) reflects the network-accessible attack vector (AV:N), low attack complexity (AC:L), and lack of required privileges (PR:N) or user interaction (UI:N), though impact is limited to availability (A:H). The availability of a public proof-of-concept exploit substantially elevates the threat, as adversaries can readily weaponize the vulnerability without developing custom exploits. The unauthenticated remote attack vector means any network-accessible strongSwan deployment running IKEv2 with EAP-TTLS is exposed to opportunistic scanning and exploitation. From an SSVC perspective, this vulnerability is automatable (can be exploited without human interaction per target), has technical impact limited to denial of service, and has confirmed public exploit code. While not appearing in CISA KEV (suggesting no observed mass exploitation campaigns yet), the combination of public exploit availability, network accessibility, and widespread strongSwan deployment in enterprise VPN infrastructure makes this a genuine priority for organizations using affected versions, particularly those with internet-facing VPN gateways.
Exploit ScenarioDerived

An unauthenticated remote attacker scans the internet for strongSwan VPN gateways listening on UDP port 500 (IKEv2). Upon identifying a target running a vulnerable version, the attacker uses the publicly available proof-of-concept exploit to initiate an IKEv2 authentication exchange and sends specially crafted EAP-TTLS AVP packets containing manipulated length fields designed to trigger integer underflow during parsing. The malformed length values cause the charon daemon to attempt invalid memory operations, resulting in a NULL pointer dereference or memory corruption that crashes the IKE daemon, denying VPN service to legitimate users until administrators manually restart the service.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 23, 2026

Unauthenticated remote attackers can crash strongSwan versions 4.5.0 through 6.0.4 via integer underflow in the EAP-TTLS AVP parser during IKEv2 authentication by sending malformed AVP packets with invalid length fields. Public exploit code exists for this denial of service vulnerability, which triggers memory corruption in the charon daemon with no available patch. Organizations running affected strongSwan versions are vulnerable to service disruption without authentication or user interaction required.

Earlier versions of this analysis (1)
v1 Mar 23, 2026 - 19:00 CVSS 8.7

An integer underflow vulnerability exists in the EAP-TTLS AVP parser of strongSwan versions 4.5.0 through 6.0.4, allowing unauthenticated remote attackers to crash the charon IKE daemon and cause denial of service. The vulnerability is exploitable over the network with low complexity and requires no privileges or user interaction. A publicly available proof-of-concept exploit exists, significantly increasing the real-world risk to affected deployments.

RemediationAI

Upgrade to strongSwan version 6.0.5 or later, which addresses the integer underflow vulnerability in the EAP-TTLS AVP parser. The patch release is documented at https://www.strongswan.org/blog/2026/03/23/strongswan-6.0.5-released.html. Organizations unable to immediately upgrade should consider implementing network-level protections such as restricting VPN gateway access to trusted IP ranges via firewall rules, deploying intrusion prevention system (IPS) signatures to detect malformed AVP packets if available, or temporarily disabling EAP-TTLS authentication in favor of alternative IKEv2 authentication methods if operationally feasible. Given the availability of public exploit code and the unauthenticated remote nature of the attack, patching should be prioritized for all internet-facing strongSwan VPN deployments.

Affected VersionsENISA

strongSwan 4.5.0 <6.0.5

Affected Packages

euvd strongswan fix: 6.0.5

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

strongSwan is a widely-deployed open-source IPsec-based VPN solution that supports IKEv2 (Internet Key Exchange version 2) authentication. The affected component is the EAP-TTLS (Extensible Authentication Protocol - Tunneled Transport Layer Security) Attribute-Value Pair (AVP) parser, which processes authentication data during IKEv2 session establishment. The vulnerability stems from CWE-191 (Integer Underflow/Wraparound), where the parser fails to validate AVP length fields before performing subtraction operations. This allows specially crafted AVP data with malicious length values to trigger integer underflow, leading to excessive memory allocation attempts or NULL pointer dereferences that crash the charon daemon process. The affected product per CPE string is cpe:2.3:a:strongswan:strongswan across a wide range of versions spanning multiple major releases.

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Severity by source

Vendor (VulnCheck) PRIMARY 8.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CIRCL (temporal) 7.5 HIGH
Ubuntu MEDIUM
SUSE 7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
None
Vulnerable system: Integrity
None
Vulnerable system: Availability
High
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

Lifecycle Timeline

3
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
PoC Detected
Mar 27, 2026 - 20:16 vuln.today
Public exploit code
CVE Published
Mar 23, 2026 - 18:33 nvd
HIGH 8.7

DescriptionCVE.org

strongSwan versions 4.5.0 prior to 6.0.5 contain an integer underflow vulnerability in the EAP-TTLS AVP parser that allows unauthenticated remote attackers to cause a denial of service by sending crafted AVP data with invalid length fields during IKEv2 authentication. Attackers can exploit the failure to validate AVP length fields before subtraction to trigger excessive memory allocation or NULL pointer dereference, crashing the charon IKE daemon.

Executive ViewAI

Why It Matters

strongSwan versions 4.5.0 through 6.0.4 contain a critical denial-of-service vulnerability that allows remote attackers to crash IKE daemon services without authentication. Organizations using affected versions face immediate risk of VPN service disruption, with active exploits in the wild and no vendor patch currently available.

Business Impact: High
Compensating Controls

Implement network-level access controls to restrict UDP ports 500 and 4500 to only authorized VPN gateway peers; deploy IDS/IPS signatures to detect malformed EAP-TTLS AVP packets; disable EAP-TTLS authentication method if not required and use alternative EAP methods; implement automatic charon process restart/monitoring to limit DoS impact duration; segment VPN infrastructure to isolate affected instances; monitor for CVE-2026-25075 POC exploit signatures and block suspicious EAP-TTLS traffic patterns at firewall.

Threat Intelligence Overview

EPSS Score
0.1%
Top 70% exploitable
Exploit
POC
Public exploit code exists
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC Yes
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
High
Technical Impact
Partial

Priority Score

64
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +44
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Integer Overflow MEDIUM

Integer overflow occurs when an arithmetic operation produces a result that exceeds the maximum value a given integer type can store.

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

More in Strongswan

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9.8 Dec 07

strongSwan before 5.9.12 has a buffer overflow and possible unauthenticated remote code execution via a DH public value

CVE-2023-26463 CRITICAL
9.8 Apr 15

strongSwan 5.9.8 and 5.9.9 potentially allows remote code execution because it uses a variable named "public" for two di
CVE-2013-5018 MEDIUM POC
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The is_asn1 function in strongSwan 4.1.11 through 5.0.4 does not properly validate the return value of the asn1_length f
CVE-2017-9022 HIGH
7.5 Jun 08

The gmp plugin in strongSwan before 5.5.3 does not properly validate RSA public keys before calling mpz_powm_sec, which

CVE-2017-9023 HIGH
7.5 Jun 08

The ASN.1 parser in strongSwan before 5.5.3 improperly handles CHOICE types when the x509 plugin is enabled, which allow
CVE-2017-11185 HIGH
7.5 Aug 18

The gmp plugin in strongSwan before 5.6.0 allows remote attackers to cause a denial of service (NULL pointer dereference
CVE-2012-2388 HIGH
7.5 Jun 27

The GMP Plugin in strongSwan 4.2.0 through 4.6.3 allows remote attackers to bypass authentication via a (1) empty or (2)
CVE-2026-78133 HIGH
7.5 Sep 07

Use-after-free in strongSwan's IKEv2 Multi-Key Exchange (Multi-KE, RFC 9370) implementation is triggered when two authen
CVE-2026-78130 HIGH
7.5 Sep 07

Denial of service via NULL-pointer dereference in strongSwan's x509 plugin affects versions 4.2.0 through 6.0.x, trigger
CVE-2026-78132 HIGH
7.5 Sep 07

Denial of service via infinite loop in strongSwan's x509 plugin affects all deployments that process X.509 attribute cer
CVE-2026-25998 HIGH
7.5 Feb 19

strongMan's credential encryption uses a static initialization vector with AES-CTR mode, causing all database fields to

Same weakness CWE-191 – Integer Underflow

View all
CVE-2014-0497 CRITICAL POC
9.8
CVE-2015-5212 MEDIUM
6.8
CVE-2017-14496 HIGH POC
7.5
CVE-2014-8768 MEDIUM POC
5.0
CVE-2017-11757 CRITICAL POC
9.8
CVE-2024-23313 CRITICAL POC
9.8
CVE-2021-3323 CRITICAL POC
9.8
CVE-2021-21811 CRITICAL POC
9.8

Same technique Denial Of Service

View all
CVE-2015-5119 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2011-0611 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8
CVE-2012-0507 CRITICAL POC
9.8
CVE-2014-1761 HIGH POC
7.8
CVE-2015-5122 CRITICAL POC
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CVE-2011-0609 HIGH POC
7.8

Vendor StatusVendor

Ubuntu

Priority: Medium
strongswan
Release Status Version
trusty needs-triage -
xenial needs-triage -
bionic needs-triage -
focal needs-triage -
upstream released 6.0.5
jammy released 5.9.5-2ubuntu2.5
noble released 5.9.13-2ubuntu4.24.04.2
questing released 6.0.1-6ubuntu4.2
USN-8117-1

Debian

strongswan
Release Status Fixed Version Urgency
bullseye vulnerable 5.9.1-1+deb11u4 -
bullseye (security) vulnerable 5.9.1-1+deb11u5 -
bookworm fixed 5.9.8-5+deb12u3 -
bookworm (security) fixed 5.9.8-5+deb12u3 -
trixie fixed 6.0.1-6+deb13u4 -
trixie (security) fixed 6.0.1-6+deb13u4 -
forky, sid vulnerable 6.0.4-1 -
(unstable) fixed (unfixed) -
DSA-6176-1

SUSE

Severity: High
Product Status
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Fixed

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-25075 ADVISORY https://security-tracker.debian.org/tracker/dsa-6176-1 ADVISORY https://ubuntu.com/security/notices/USN-8117-1 ADVISORY https://vuldb.com/?id.352574 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0978/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0979/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0980/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0981/ REF https://lists.debian.org/debian-lts-announce/2026/03/msg00016.html REF https://www.strongswan.org/blog/2026/03/23/strongswan-6.0.5-released.html REF https://www.vulncheck.com/advisories/strongswan-eap-ttls-avp-parsing-integer-underflow REF https://y637f9qq2x.com/posts/cve-2026-25075/

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