CVE-2026-40356

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Important Important Impact What does this mean?
5.9 CVSS v3 Base Score

Description

A flaw was found in MIT Kerberos 5 (krb5). An unauthenticated remote attacker can exploit an integer underflow and an out-of-bounds read vulnerability by calling gss_accept_sec_context() on a system with a NegoEx mechanism registered. This can lead to the process terminating, resulting in a Denial of Service (DoS).

Statement

An Important denial of service vulnerability exists in MIT Kerberos 5, allowing an unauthenticated remote attacker to terminate processes. This occurs on systems where the NegoEx mechanism is registered and an application invokes gss_accept_sec_context(), leading to an integer underflow and out-of-bounds read.

Mitigation

To mitigate this issue, ensure that the NegoEx mechanism is not registered in the `/etc/gss/mech` configuration file. Removing the corresponding entry from this file will prevent the vulnerable code path from being activated. This action may impact services that rely on the NegoEx GSS-API mechanism. A restart of affected Kerberos-dependent services may be required for the change to take effect.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2026-40356

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2026-40356

Content from cems.fun is not included.https://cems.fun/2026/04/27/krb5-two-unauthenticated-network-vulnerabilities.html

Content from github.com is not included.https://github.com/krb5/krb5/commit/2e75f0d9362fb979f5fc92829431a590a130929f

Content from web.mit.edu is not included.https://web.mit.edu/kerberos/advisories/

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 10 krb5 Fixed RHSA-2026:19145
Red Hat Enterprise Linux 6 krb5 Fix deferred
Red Hat Enterprise Linux 7 krb5 Fix deferred
Red Hat Enterprise Linux 8 krb5 Fixed RHSA-2026:16799
Red Hat Enterprise Linux 9 krb5 Fixed This content is not included.RHSA-2026:19357
Red Hat Hardened Images krb5-main Fixed RHSA-2026:12220
Red Hat OpenShift Container Platform 4 rhcos Fix deferred
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 5.9
Attack Vector Network
Attack Complexity High
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Impact None
Integrity Impact None
Availability Impact High

CVSS v3 Vector

Red Hat CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.

My product is listed as "Out of Support Scope". What does this mean?

 When a product is listed as "Out of Support Scope", it means a vulnerability with the impact level assigned to this CVE is no longer covered by its current support lifecycle phase. The product has been identified to contain the impacted component, but analysis to determine whether it is affected or not by this vulnerability was not performed. The product should be assumed to be affected. Customers are advised to apply any mitigation options documented on this page, consider removing or disabling the impacted component, or upgrade to a supported version of the product that has an update available.