Detect Ccache Files in Splunk
Adversaries may attempt to steal Kerberos tickets stored in credential cache (ccache) files. These files store short-lived Kerberos session credentials created at authentication, enabling access to network services without re-entering passwords. On Linux, ccache files are typically located in /tmp with names in the format krb5cc_<UID> or krb5.ccache; storage is governed by the KRB5CCNAME environment variable and /etc/krb5.conf. On macOS, ccache entries are held in memory under an API:{uuid} naming scheme, accessible via lower-level Kerberos framework APIs. Adversaries steal these files and replay tickets to authenticate as the victim without knowing their password (Pass the Ticket). Impacket tools including getST.py, getTGT.py, and ticketer.py are commonly used to programmatically interact with ccache files. Kekeo can convert ccache files to Windows kirbi format for reuse on Windows systems, enabling cross-platform lateral movement. Real-world usage includes APT groups operating in Active Directory environments with Linux-integrated systems.
MITRE ATT&CK
- Tactic
- Credential Access
- Technique
- T1558 Steal or Forge Kerberos Tickets
- Sub-technique
- T1558.005 Ccache Files
- Canonical reference
- https://attack.mitre.org/techniques/T1558/005/
SPL Detection Query
index=linux sourcetype="linux_audit"
| eval _is_ccache_key = if(isnotnull(key) AND key="kerberos_ccache", 1, 0)
| eval _is_impacket = if(
match(coalesce(exe, ""), "(getST|getTGT|ticketer|getNTHash|rbcd|getServiceTicket|getPac)[.]py$"), 1, 0)
| eval _is_python_kerb = if(
match(coalesce(exe, ""), "python[0-9]?$") AND
(match(_raw, "CCache") OR match(_raw, "krb5cc_") OR match(_raw, "KRB5CCNAME") OR match(_raw, "[.]ccache")), 1, 0)
| eval _is_copy_exfil = if(
match(coalesce(exe, ""), "/(cp|mv|cat|base64|xxd|tar|scp|rsync|ncat?|curl|wget|dd)$") AND
(match(_raw, "krb5cc_[0-9]+") OR match(_raw, "krb5[.]ccache")), 1, 0)
| where _is_ccache_key=1 OR _is_impacket=1 OR _is_python_kerb=1 OR _is_copy_exfil=1
| where NOT match(coalesce(exe, ""), "(kinit|klist|kdestroy|sssd|krb5kdc|kadmind|sshd|login)$")
| eval detection_type = case(
_is_impacket=1, "ImpacketKerberosTool",
_is_python_kerb=1, "PythonKerberosInteraction",
_is_copy_exfil=1, "CcacheFileCopyOrExfiltration",
_is_ccache_key=1, "CcacheFileAccess",
true(), "KerberosActivityUnknown")
| table _time, host, uid, auid, exe, comm, key, name, pid, ppid, syscall, detection_type
| sort - _timeDetects ccache file theft using Linux auditd data ingested via the Splunk Add-on for Unix and Linux (linux_audit sourcetype). Four detection branches: (1) events matching an auditd file watch rule with key=kerberos_ccache on /tmp/krb5cc_* paths, (2) Impacket Kerberos tool execution, (3) Python processes referencing ccache objects, and (4) shell utilities copying or encoding ccache files. Requires auditd to be configured with a file watch rule: -a always,exit -F dir=/tmp -F name_format=krb5cc_% -k kerberos_ccache (or equivalent watch rule). Excludes legitimate Kerberos system processes to reduce noise.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Backup agents performing filesystem-level scans of /tmp will generate ccache_key events if the auditd watch covers the full /tmp directory
- Legitimate Python Kerberos applications (Hadoop ecosystem, MIT Kerberos bindings via gssapi library) performing routine ticket operations
- Security scanners like Lynis or rkhunter that inspect /tmp contents as part of filesystem audits
- Administrators running klist or manual ccache file operations during Kerberos troubleshooting sessions
- Container orchestration systems (Kubernetes with Kerberos sidecar containers) that routinely renew and access ccache files for pod authentication
Other platforms for T1558.005
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Discover and Copy Ccache File
Expected signal: DeviceProcessEvents: process creation for find (/tmp/krb5cc_*), klist (-c /tmp/krb5cc_<uid>), and cp. DeviceFileEvents: FileCreated for /tmp/.svc_cache_bak with InitiatingProcessFileName=cp. Auditd (linux_audit): SYSCALL records for open/read on /tmp/krb5cc_<uid> with exe=/bin/cp, plus PATH records for both source and destination files. key=kerberos_ccache if auditd watch is configured.
- Test 2Base64 Encode Ccache for Exfiltration
Expected signal: DeviceProcessEvents: process creation for base64 with ProcessCommandLine containing 'krb5cc_<uid>' and xxd with the same path. Auditd (linux_audit): SYSCALL open/read records on /tmp/krb5cc_<uid> with exe=/usr/bin/base64 and exe=/usr/bin/xxd. These processes will appear in linux_audit events alongside EXECVE records showing the full command.
- Test 3Use Impacket Python Library to Read Ccache Tickets
Expected signal: DeviceProcessEvents: python3 process creation with ProcessCommandLine containing 'CCache', 'ccache', 'krb5cc_'. DeviceFileEvents: FileRead event on /tmp/krb5cc_<uid> with InitiatingProcessFileName=python3. Auditd (linux_audit): SYSCALL open record with exe=/usr/bin/python3 on the ccache path. EXECVE record showing full python3 -c invocation with ccache string patterns.
- Test 4Set KRB5CCNAME to Stolen Ticket and Authenticate
Expected signal: DeviceProcessEvents: cp process with /tmp/krb5cc_<uid> in command line, klist process with -c /tmp/attacker_krb5cc argument. DeviceFileEvents: FileCreated for /tmp/attacker_krb5cc with InitiatingProcessFileName=cp. Auditd (linux_audit): SYSCALL records for cp (open/read on source, open/write/creat on destination) and klist (open/read on /tmp/attacker_krb5cc). The unusual ccache path /tmp/attacker_krb5cc is a behavioral anomaly.
References (12)
- https://attack.mitre.org/techniques/T1558/005/
- https://www.binarydefense.com/resources/blog/shining-a-light-in-the-dark-how-binary-defense-uncovered-an-apt-lurking-in-shadows-of-it/
- https://adepts.of0x.cc/kerberos-thievery-linux/
- https://posts.specterops.io/when-kirbi-walks-the-bifrost-4c727807744f
- https://www.fireeye.com/blog/threat-research/2020/04/kerberos-tickets-on-linux-red-teams.html
- https://labs.portcullis.co.uk/download/eu-18-Wadhwa-Brown-Where-2-worlds-collide-Bringing-Mimikatz-et-al-to-UNIX.pdf
- https://github.com/gentilkiwi/kekeo
- https://github.com/fortra/impacket
- https://web.mit.edu/kerberos/krb5-1.12/doc/basic/ccache_def.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1558.005/T1558.005.md
- https://learn.microsoft.com/en-us/defender-endpoint/linux-support-events
- https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/using_kerberos/introduction-to-kerberos_using-kerberos
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