Delinea Secret Server CVE-2026-15638

Exploitation requires network reachability to an on-prem Delinea Secret Server (versions 10.5.1 through 12.1.3) exposing a cryptographic operation that leaks padding-validation state; per CVSS PR:N/UI:N no authentication or user interaction is needed. Limiting factors are significant: the attack is a complex adaptive chosen-ciphertext (padding oracle) technique (AC:H) with an attack requirement (AT:P), meaning it needs many crafted requests, observable distinguishable responses, and the specific vulnerable oracle behavior - it is not a single-request exploit. It applies only to the on-prem product line, not necessarily cloud-hosted deployments, and does not itself expose the cryptographic key.

The vendor CVSS 4.0 base score is 9.1 (Critical), driven largely by high subsequent-system impact (SC:H/SI:H/SA:H) - reflecting that a padding oracle lets an attacker abuse the server's own cryptographic key to decrypt or forge data protected across the system, not just the vulnerable endpoint. However, the base vector itself tempers this: AV:N but AC:H and AT:P mean the attack is a complex, adaptive chosen-ciphertext attack requiring specific conditions and many probing requests, not a trivial one-shot exploit. PR:N/UI:N confirms it is reachable by an unauthenticated user who can reach Secret Server. Real-world urgency signals are LOW and consistent with each other: EPSS is only 0.20% (10th percentile), there is no CISA KEV listing, and no public POC was identified - so this is currently a high-severity-by-design cryptographic flaw rather than a demonstrably weaponized one. Note the input CWE-327 (broken/risky crypto algorithm) is the correct root-cause class for a padding oracle (arguably CWE-347/CWE-208 could also apply). No conflicting signals on attack vector - CVSS network vector aligns with the description's 'access to Secret Server.' Net: patch on a prioritized-but-not-emergency basis given the sensitivity of a secrets vault, tempered by high attack complexity and absence of exploitation evidence.

An unauthenticated attacker who can reach an on-prem Secret Server instance (10.5.1 through 12.1.3) sends a stream of manipulated ciphertexts to a cryptographic endpoint and observes padding-validation responses, using the differences as an oracle to decrypt protected data or to encrypt/forge data with the server's key without ever extracting the key itself. Because the attack is an adaptive chosen-ciphertext technique, it requires many requests and specific conditions (reflected in AC:H/AT:P). No public exploit code was identified at the time of analysis.