CVE-2025-4166
📋 TL;DR
CVE-2025-4166 allows sensitive information exposure in Vault server and audit logs when users submit malformed payloads during secret creation or update operations via the KV v2 plugin REST API. This affects Vault Community and Vault Enterprise users who process malformed data through the KV v2 endpoints. Attackers could potentially retrieve secrets that should remain confidential.
💻 Affected Systems
- Vault Community
- Vault Enterprise
📦 What is this software?
Openbao by Openbao
Vault by Hashicorp
Vault by Hashicorp
Vault by Hashicorp
Vault by Hashicorp
Vault by Hashicorp
⚠️ Risk & Real-World Impact
Worst Case
Sensitive secrets like passwords, API keys, or certificates are exposed in logs accessible to unauthorized personnel, leading to credential theft and lateral movement.
Likely Case
Partial secret exposure in error logs that could be combined with other information to compromise systems or accounts.
If Mitigated
Limited exposure of non-critical data fragments with proper log access controls and monitoring in place.
🎯 Exploit Status
Exploitation requires sending malformed payloads to KV v2 endpoints; no authentication needed if API access is available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Vault Community 1.19.3, Vault Enterprise 1.19.3, 1.18.9, 1.17.16, 1.16.20
Vendor Advisory: https://discuss.hashicorp.com/t/hcsec-2025-09-vault-may-expose-sensitive-information-in-error-logs-when-processing-malformed-data-with-the-kv-v2-plugin
Restart Required: Yes
Instructions:
1. Backup Vault configuration and data. 2. Download patched version from HashiCorp releases. 3. Stop Vault service. 4. Replace binary with patched version. 5. Restart Vault service. 6. Verify version and functionality.
🔧 Temporary Workarounds
Restrict KV v2 API Access
allLimit access to KV v2 endpoints using Vault policies or network controls to reduce attack surface.
vault policy write restrict-kv - <<EOF
path "secret/data/*" {
capabilities = ["deny"]
}
EOF
Enhanced Log Filtering
allConfigure log filtering to exclude sensitive error details from being written to logs.
# Configure in Vault config file:
log_level = "INFO"
# Or use external log processing tools
🧯 If You Can't Patch
- Implement strict access controls on log storage and review who can access Vault logs
- Monitor KV v2 API endpoints for malformed request patterns and implement rate limiting
🔍 How to Verify
Check if Vulnerable:
Check Vault version: if running affected versions and using KV v2 plugin, system is vulnerable.Check Version:
vault versionVerify Fix Applied:
Confirm version is patched and test that malformed KV v2 requests no longer expose secrets in logs.📡 Detection & Monitoring
Log Indicators:
- Error logs containing secret fragments or sensitive data
- Unusual malformed request patterns to KV v2 endpoints
Network Indicators:
- Multiple malformed POST/PUT requests to /v1/secret/data/* endpoints
- Unusual error response patterns from Vault API
SIEM Query:
source="vault" AND ("malformed" OR "error") AND ("secret" OR "kv" OR "data")