Denial of Service via sending bogus X.509 certificates
Summary
| CVE | CVE-2026-77205 |
|---|---|
| State | PUBLISHED |
| Assigner | libreswan |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-13 22:18:24 UTC |
| Updated | 2026-10-16 19:55:59 UTC |
| Description | Libreswan in FIPS mode has a vulnerability where badly formed received certificates are rejected, but not deleted from the NSS cache. As a result, any real certificates with the same serial number are rejected as well. This can be abused to lock out legitimate peers from connecting. The add_decoded_cert() function missed a call to CERT_DestroyCertificate() due to an incorrect fix for CVE-2026-14957. Sending bogus certificates with new serial numbers could prevent the real certificates with those serial numbers from connecting until the service has restarted. |
Risk And Classification
Primary CVSS: v3.1 3.7 LOW from d42dc95b-23f1-4e06-9076-20753a0fb0df
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS: 0.001830000 probability, percentile 0.073620000 (date 2026-10-16)
Problem Types: CWE-772 | CWE-772 CWE-772: Missing Release of Resource after Effective Lifetime
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | d42dc95b-23f1-4e06-9076-20753a0fb0df | Secondary | 3.7 | LOW | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L |
| 3.1 | CNA | CVSS | 3.7 | LOW | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L |
CVSS v3.1 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | The Libreswan Project | Libreswan | affected 5.3 5.3.2 semver | Not specified |
| CNA | The Libreswan Project | Libreswan | unaffected 5.3.3 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| libreswan.org/security/CVE-2026-14957/CVE-2026-14957.txt | d42dc95b-23f1-4e06-9076-20753a0fb0df | libreswan.org | |
| libreswan.org/security/CVE-2026-77205 | d42dc95b-23f1-4e06-9076-20753a0fb0df | libreswan.org | |
| libreswan.org/security/CVE-2026-77205/CVE-2026-77205.txt | d42dc95b-23f1-4e06-9076-20753a0fb0df | libreswan.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Wojciech Tatarski (TuxCare) (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-07-30T00:00:00.000Z | Libreswan was notified of the issue via [email protected] |
| CNA | 2026-09-24T00:00:00.000Z | Advanced notice given to supported customers and distributions |
| CNA | 2026-10-05T00:00:00.000Z | Public announcement and release of libreswan 5.3.3 |
Solutions
CNA: Upgrade to libreswan 5.3.3 or later. Patches are available at https://libreswan.org/security/CVE-2026-77205/
Workarounds
CNA: Disabling FIPS mode will prevent this attack vector. If this is not possible, upgrade to a later libreswan version or apply the available patch.
Exploits
CNA: No known exploitation in the wild. An attacker could trick a peer into connecting to them first to learn the serial number, then use that to prevent the peer from connecting to the legitimate server. Exploitation requires FIPS mode to be enabled.