Medium [CVE-2026-58216] kpasswd service: kpasswd packet that contains malformed ASN.1 might cause the server to access 6 bytes of unallocated memory leading server to crash
This medium-severity Red Hat Linux advisory covers CVE-2026-58216.
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Summary
An out-of-bounds read flaw was found in Samba's Kerberos Key Distribution Center's (KDC) password change (kpasswd) service. When processing malformed ASN.1-encoded Kerberos password change request, Samba server miscalculates the structure size and attempts to read up to six bytes beyond the end of the allocated buffer.
While this out-of-bounds read typically results in a harmless decryption failure, if the read hits unmapped memory, it causes the KDC process to crash.
An authenticated attacker can send a specially crafted kpasswd request containing malformed ASN.1 data to trigger the out-of-bounds read, which may cause the KDC process to terminate, resulting in a denial of service. Red Hat Product Security has rated this vulnerability as having a Moderate security impact.
Successful exploitation requires an authenticated attacker to craft a malformed ASN.1-encoded Kerberos password change request that precisely triggers the underlying parsing flaw, increasing the attack complexity.
The Samba project also notes that the attack is unreliable in practice and an attacker may need to perform numerous kpasswd attempts before successfully causing the service to terminate. ``` Standard RHEL Server Deployments (Not Affected): Default Red Hat Enterprise Linux (RHEL) deployments are not affected.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 23 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 23 days ago·verify at source
Mitigation checklist
- Administrators who do not require the Kerberos password change service may disable it by setting ```kpasswd port = 0``` in ```/etc/samba/smb.conf```. Where disabling the service is not practical, rate-limiting access to the kpasswd service may reduce the likelihood of successful exploitation until an updated package can be applied. Note: Disabling kpasswd port will prevent domain users from changing their Kerberos passwords via the kpasswd protocol until patched.
Official advisory · high-confidence parse· fetched 23 days ago·verify at source
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