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CVE-2026-15638 – Cryptographic Padding Oracle – Delinea Secret Server (On-Prem) 10.5.1–12.1.3

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Summary

CVE-2026-15638 is a cryptographic padding oracle vulnerability (CWE-327: Use of a Broken or Risky Cryptographic Algorithm) affecting on-premises Delinea Secret Server for Windows. An unauthenticated attacker with network access to a vulnerable instance can exploit the padding oracle to decrypt or encrypt data using one of the server’s cryptographic keys, without exposing the key itself. The issue carries a CVSS v4.0 base score of 9.1 (Critical).

Technical details

  • Root cause: The application uses a broken or risky cryptographic construction that is susceptible to a padding oracle attack (CAPEC-463), where distinguishable error responses to malformed ciphertext allow an attacker to iteratively recover plaintext or forge valid ciphertext.
  • Trigger conditions: An attacker only needs network reachability to the Secret Server application; no authentication or user interaction is required, though the CVSS vector indicates attack conditions must be present (AT:P) and attack complexity is high (AC:H).
  • Attack vector: Network (remote, unauthenticated).
  • Impact: An attacker can leverage the padding oracle to decrypt or encrypt data protected by one of the server’s cryptographic keys. The underlying cryptographic key material itself is not disclosed, but confidentiality and integrity of data protected by that key can be compromised.

Affected software

  • Delinea Secret Server (On-Prem), Windows platform — versions 10.5.1 through 12.1.3 (inclusive).
  • Delinea Secret Server Cloud is not listed as affected.

Severity

  • CVSS v4.0 Base Score: 9.1 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:H/SA:H

Mitigation and recommended actions

  • Immediate: Upgrade Secret Server (On-Prem) to version 12.2.7 or later, which resolves this vulnerability.
  • If no patch can be applied immediately: Restrict network access to the Secret Server management interface to trusted internal networks or VPN only, and monitor for anomalous cryptographic-error or repeated-request patterns that may indicate padding-oracle probing, until the upgrade can be completed.

References

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