# CVE-2026-25075: strongSwan integer underflow in EAP-TTLS AVP parser

Source: https://junglewise.ai/threats/cve-2026-25075-strongswan-integer-underflow-in-eap-ttls-avp-parser  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-23. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-25075 · Severity: high · CVSS 7.5 · Published 2026-03-23

strongSwan is a widely used open-source software for creating secure VPN connections. A flaw in how it handles certain authentication messages allows an unauthenticated remote attacker to crash the VPN service. This results in a denial of service, preventing users from connecting to the network and disrupting secure communications.

Technologies: [strongSwan](https://junglewise.ai/threats/technologies/strongswan). Vendors: [strongSwan](https://junglewise.ai/threats/vendors/strongswan).

## Quick answers

**Is CVE-2026-25075 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-25075 being exploited in the wild.

**How severe is CVE-2026-25075?** High severity, with a CVSS score of 7.5, published 23 March 2026.

**Which products and versions are affected?** strongSwan 4.5.0 prior to 6.0.5.

**Is there a fix for CVE-2026-25075?** A patch was published on 2026-03-23: strongSwan 6.0.5 released with fix Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-25075 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-25075?** Check whether you run strongSwan at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer underflow vulnerability exists in the eap-ttls plugin of strongSwan when processing Attribute-Value Pairs (AVPs). The parser fails to validate that the 3-byte length field in the AVP header is at least 8 bytes (the size of the header itself) before subtracting 8 to determine the payload length. By sending a crafted AVP with a length between 0 and 7, an unauthenticated remote attacker triggers a 32-bit integer underflow. This leads to an extremely large memory allocation attempt (~4 GiB) via chunk_alloc(). Because the software does not verify if the allocation succeeded before attempting to write to the resulting buffer, a NULL pointer dereference occurs, crashing the charon IKE daemon. The vulnerability is reachable during the IKEv2 authentication phase before the client has authenticated. Fixed in version 6.0.5.

## Affected products

- strongSwan strongSwan 4.5.0 prior to 6.0.5

## Timeline

- 2026-03-23: disclosed: Vulnerability reported by Kazuma Matsumoto
- 2026-03-23: patched: strongSwan 6.0.5 released with fix
- 2026-03-23: advisory

## References

- [https://www.strongswan.org/blog/2026/03/23/strongswan-6.0.5-released.html](https://www.strongswan.org/blog/2026/03/23/strongswan-6.0.5-released.html)
- [https://www.strongswan.org/blog/2026/03/23/strongswan-vulnerability-(cve-2026-25075).html](https://www.strongswan.org/blog/2026/03/23/strongswan-vulnerability-(cve-2026-25075).html)
- [https://www.vulncheck.com/advisories/strongswan-eap-ttls-avp-parsing-integer-underflow](https://www.vulncheck.com/advisories/strongswan-eap-ttls-avp-parsing-integer-underflow)
- [https://y637f9qq2x.com/posts/cve-2026-25075/](https://y637f9qq2x.com/posts/cve-2026-25075/)
- [https://lists.debian.org/debian-lts-announce/2026/03/msg00016.html](https://lists.debian.org/debian-lts-announce/2026/03/msg00016.html)

## Related threats

- [strongSwan libcharon authentication bypass in IKEv2 CREATE_CHILD_SA handling](https://junglewise.ai/threats/cve-2026-78135-strongswan-libcharon-authentication-bypass-in-ikev2-create-child)
- [strongSwan incorrect identity binding in EAP-PEAP and EAP-TTLS](https://junglewise.ai/threats/cve-2026-78134-strongswan-incorrect-identity-binding-in-eap-peap-and-eap-ttls)
- [strongSwan libcharon use-after-free in IKEv2 rekeying collision handling](https://junglewise.ai/threats/cve-2026-78133-strongswan-libcharon-use-after-free-in-ikev2-rekeying-collision)
- [strongSwan x509 plugin infinite loop in ietfAttrSyntax parsing](https://junglewise.ai/threats/cve-2026-78132-strongswan-x509-plugin-infinite-loop-in-ietfattrsyntax-parsing)
- [strongSwan x509 plugin memory leak in attribute certificate parsing](https://junglewise.ai/threats/cve-2026-78131-strongswan-x509-plugin-memory-leak-in-attribute-certificate)