Vulnerability · Published Apr 28, 2026 · Assigned by mitre
CVE-2026-40355
Medium 5.9
In plain English
A medium-severity null pointer dereference in Kerberos 5 from MIT. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.6%top 48.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official description
In MIT Kerberos 5 (aka krb5) before 1.22.3, there is a NULL pointer dereference if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An unauthenticated remote attacker can trigger this, causing the process to terminate in parse_nego_message.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | krb5-devel | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-devel | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-devel | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-libs | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-libs | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-libs | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-pkinit | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-pkinit | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-pkinit | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-server | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-server | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-server | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-server-ldap | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-server-ldap | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-server-ldap | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-workstation | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | krb5-workstation | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | krb5-workstation | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | krb5-xrealmauthz | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:9 | krb5-xrealmauthz | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| AlmaLinux:10 | libkadm5 | 1.21.3-10.el10_2 | ALSA-2026:19145 |
| AlmaLinux:8 | libkadm5 | 1.18.2-34.el8_10 | ALSA-2026:16799 |
| AlmaLinux:9 | libkadm5 | 1.21.1-10.el9_8 | ALSA-2026:19357 |
| Debian:12 | krb5 | 1.20.1-2+deb12u5 | DEBIAN-CVE-2026-40355 |
| Debian:13 | krb5 | 1.21.3-5+deb13u1 | DEBIAN-CVE-2026-40355 |
| Debian:14 | krb5 | 1.22.1-2.1 | DEBIAN-CVE-2026-40355 |
| Rocky Linux:10 | krb5 | 0:1.21.3-10.el10_2 | RLSA-2026:19145 |
| Rocky Linux:8 | krb5 | 0:1.18.2-34.el8_10 | RLSA-2026:16799 |
| Rocky Linux:9 | krb5 | 0:1.21.1-10.el9_8 | RLSA-2026:19357 |
| Ubuntu:22.04:LTS | krb5 | 1.19.2-2ubuntu0.8 | UBUNTU-CVE-2026-40355 |
| Ubuntu:22.04:LTS | krb5 | 1.19.2-2ubuntu0.8 | USN-8585-1 |
| Ubuntu:24.04:LTS | krb5 | 1.20.1-6ubuntu2.7 | USN-8585-1 |
| Ubuntu:24.04:LTS | krb5 | 1.20.1-6ubuntu2.7 | UBUNTU-CVE-2026-40355 |
| Ubuntu:25.10 | krb5 | no fix listed | UBUNTU-CVE-2026-40355 |
| Ubuntu:26.04:LTS | krb5 | 1.22.1-2ubuntu4.1 | UBUNTU-CVE-2026-40355 |
| Ubuntu:26.04:LTS | krb5 | 1.22.1-2ubuntu4.1 | USN-8585-1 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MIT | Kerberos 5 | 1.18 – before 1.22.3 |
Weakness: CWE-476 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://web.mit.edu/kerberos/advisories/
- https://cems.fun/2026/04/27/krb5-two-unauthenticated-network-vulnerabilities.html
- https://github.com/krb5/krb5/commit/2e75f0d9362fb979f5fc92829431a590a130929f
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://cert-portal.siemens.com/productcert/html/ssa-019113.html
- https://cert-portal.siemens.com/productcert/html/ssa-457936.html