SAP patches a maximum-severity Python SDK flaw that redirects OAuth2 token requests through tenant_subdomain

The attack requires control of the tenant_subdomain value. SAP's Tuesday advisory reads: "The SAP Cloud SDK for Python contains an OAuth2 SSRF vulnerability affecting multi-tenant BTP applications. An attacker who controls the tenant_subdomain parameter can redirect OAuth2 token requests to an attacker-controlled server, causing client credentials to be exfiltrated." ^[2]

The advisory tells consumer applications to validate "tenant_subdomain against a known allowlist of registered tenant subdomains before passing it to any SDK call." ^[6] We think an app that only hands the SDK values from its own tenant registry gives an attacker nothing to redirect. An app that forwards a subdomain taken from a request is the target.

Patching stops new redirects. It does not recover a secret that has already gone to an attacker's server, so we would rotate client credentials on any app that took tenant_subdomain from outside input. The report did not disclose whether anyone has exploited CVE-2026-89111 or which SDK version carries the fix.

SAP flaws have reached attackers before. CISA has added 14 SAP flaws to its exploited-vulnerabilities catalog since November 2021 ^[9]. Three of them, about 21%, were abused in ransomware attacks ^[10]. In September, SAP fixed CVE-2026-44756 in the SAP Kernel, which Onapsis named OVERPASS, and Onapsis estimated at the time that over 10,000 internet-facing SAP systems use the vulnerable component ^[8].

Inside this month's batch, we would queue CVE-2026-89110 beside CVE-2026-89111 and CVE-2026-89108 behind them, going by the access each attacker needs first ^[12][3].