libreswan: Off-by-one Error
CVE-2026-12413 is a high-severity off-by-one error vulnerability in libreswan from The Libreswan Project, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected libreswan versions: 4.6 through 5.3. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.76% chance of exploitation within 30 days, higher than 56% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of libreswan you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on libreswan.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| The Libreswan Project | libreswan | 4.6 through 5.3 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA.
Official description
An invalidly formatted IKEv2 fragment causes the Libreswan pluto daemon to crash and restart. Continued exploitation would cause a denial of service. The function reassemble_v2_incoming_fragments() would ignore unknown outer payloads but still store these in a fixed size array msg_digest.digest[PAYLIMIT]. An off-by-one error in the assertion PASSERT(logger, md->digest_roof < elemsof(md->digest)) causes the daemon to abort. No remote code execution is possible. Any configuration that allows IKEv2 connections that do not set fragmentation=no are vulnerable. IKEv1 is not affected.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Off-by-one Error
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
How developers prevent this class of flaw
- When copying character arrays or using character manipulation methods, the correct size parameter must be used to account for the null terminator that needs to be added at the end of the array. Some examples of functions susceptible to this weakness in C include strcpy(), strncpy(), strcat(), strncat(), printf(), sprintf(), scanf() and sscanf().
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in libreswan
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Off-by-one Error vulnerabilities
- 7.6 High severity
- 7.1 High severity
- 8.6 High severity
- 9.8 Critical severity
- 7.3 High severity
- 7.5 High severity
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