CVE-2025-29809 - Insecure Storage of Sensitive Information in Windows Kerberos—How Local Attackers Can Bypass Security Controls

Windows Kerberos has long been respected as one of the key authentication security technologies in Microsoft ecosystems. However, recent discoveries have exposed a critical flaw: CVE-2025-29809. This vulnerability revolves around insecure storage of sensitive information within Windows Kerberos, making it possible for an authorized attacker to bypass important security protections on a local machine.

In this post, we'll break down what CVE-2025-29809 is, how the exploit works, and what it means for system administrators. Whether you're a security professional or a Windows power user, read on to understand this important security issue.

What Is CVE-2025-29809?

Officially identified as CVE-2025-29809, this vulnerability affects the way Kerberos—Windows' default network authentication protocol—handles sensitive credentials. Specifically, the mechanism that stores Kerberos tickets and session keys does not enforce strict security boundaries on a local device. As a result, a malicious local user with authorized access could obtain sensitive Kerberos data, such as service tickets or even Ticket Granting Tickets (TGTs).

Once in possession of this data, attackers can bypass local security features that would normally prevent escalation or lateral movement.

References

- Microsoft Security Update Guide - CVE-2025-29809
- Kerberos Authentication Overview (Microsoft Docs)

Any enterprise environment using Kerberos authentication

Note: Exploitation requires *local* access (authorized, like a regular user or service account), which means an attacker needs a valid login and cannot exploit this remotely.

How Does the Exploit Work?

Kerberos stores tickets in memory, and for performance reasons, sensitive information is cached locally. Digital security best practices say that sensitive credentials should be protected by strong access controls. However, with CVE-2025-29809, these caches may be world-readable or accessible by less-privileged users.

Log in Locally: Attacker logs onto the target system as any authorized user.

2. Access Kerberos Ticket Cache: Using built-in tools or custom scripts, the attacker reads sensitive information from the local cache.
3. Extract TGT/Tickets: Attackers extract the Kerberos TGT or service tickets and their associated encryption keys.
4. Impersonate User/Service: With the extracted ticket, attacker forges a session or impersonates the victim, bypassing local security protections.

Real-World Example With Mimikatz

Mimikatz is a well-known post-exploitation tool that demonstrates this attack by dumping Kerberos tickets from memory:

# Run as local user with command prompt

# Dump Kerberos tickets
mimikatz.exe "sekurlsa::tickets /export"

# Tickets can be imported to another host:
mimikatz.exe "kerberos::ptt ticket.kirbi"

> Warning: Running tools like Mimikatz may trigger antivirus software and should only be performed in a test lab!

What’s The Risk?

- Privilege Escalation: An attacker could move laterally in the network or escalate privileges by stealing tickets from a privileged user.

Mitigation and Recommendations

- Apply Microsoft Patches: Microsoft has released patches—install them as soon as possible! See the MSRC advisory.

- Monitor Kerberos Activity: Use security monitoring tools to detect the use or movement of Kerberos tickets (such as ‘Pass-the-Ticket’ attacks).
- Harden System Configurations: Limit which users have local administrator rights and enable memory protections like Credential Guard.

Closing Thoughts

CVE-2025-29809 serves as a crucial reminder: even foundational security protocols like Kerberos can have hidden cracks when not implemented or protected carefully. Local security matters—especially in shared or multi-user environments.

If you use Windows in your business or home, review your update management and privilege assignments. The fix is as simple as patching, but monitoring for suspicious ticket activity and limiting local access will go a long way too.

Timeline

Published on: 04/08/2025 18:16:06 UTC
Last modified on: 06/04/2025 17:53:29 UTC