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Microsoft Windows: Denial of Service via Kerberos Authentication
published 5 months ago
Summary
A security update is available for Microsoft Windows, which affects the Kerberos authentication system. This issue could cause a denial of service, making it difficult for users to access certain network resources. To protect your network, apply the latest security update as soon as possible.
What to do
- Update almalinux krb5-devel to version 1.21.3-10.el10_2.
- Update almalinux krb5-libs to version 1.21.3-10.el10_2.
- Update almalinux krb5-pkinit to version 1.21.3-10.el10_2.
- Update almalinux krb5-server to version 1.21.3-10.el10_2.
- Update almalinux krb5-server-ldap to version 1.21.3-10.el10_2.
- Update almalinux krb5-workstation to version 1.21.3-10.el10_2.
- Update almalinux krb5-xrealmauthz to version 1.21.3-10.el10_2.
- Update almalinux libkadm5 to version 1.21.3-10.el10_2.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| AlmaLinux:10 | almalinux | krb5-devel |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-libs |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-pkinit |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-server |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-server-ldap |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-workstation |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | krb5-xrealmauthz |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
| AlmaLinux:10 | almalinux | libkadm5 |
< 1.21.3-10.el10_2 Fix: upgrade to 1.21.3-10.el10_2
|
Original advisory text
Important: krb5 security update
Kerberos is a network authentication system, which can improve the security of your network by eliminating the insecure practice of sending passwords over the network in unencrypted form. It allows clients and servers to authenticate to each other with the help of a trusted third party, the Kerberos key distribution center (KDC).
Security Fix(es):
* krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read (CVE-2026-40356)
* krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism (CVE-2026-40355)
For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.
Security Fix(es):
* krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read (CVE-2026-40356)
* krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism (CVE-2026-40355)
For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.
References
- https://access.redhat.com/errata/RHSA-2026:19145 Vendor Advisory
- https://access.redhat.com/security/cve/CVE-2026-40355 Third Party Advisory
- https://access.redhat.com/security/cve/CVE-2026-40356 Third Party Advisory
- https://bugzilla.redhat.com/2463368 Third Party Advisory
- https://bugzilla.redhat.com/2463370 Third Party Advisory
- https://errata.almalinux.org/10/ALSA-2026-19145.html Vendor Advisory
Timeline
Published19 May 2026
Updated26 May 2026
First seen26 May 2026
Sources
ALSA-2026:19145 · OSV
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