Bug 2572590 (CVE-2026-127099)

Summary: CVE-2026-127099 sssd: sssd: Stack buffer overflow during RSA certificate-to-SSH key conversion
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, security-response-team, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in SSSD's conversion of X.509 certificate RSA public keys to SSH keys. Missing size checks before copying RSA components into fixed-size stack buffers can cause a stack buffer overflow. An attacker able to supply a certificate with oversized RSA components that passes the configured certificate checks can cause denial of service and corrupt SSH responder memory.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2572656    
Bug Blocks:    

Description OSIDB Bzimport 2026-11-12 15:00:23 UTC 
A flaw was found in SSSD. The rsa_pub_key_to_ssh() function in src/util/cert/libcrypto/cert.c converts the RSA modulus and public exponent from an X.509 certificate into fixed-size stack buffers using BN_bn2bin(), without checking BN_num_bytes() against the destination sizes. The exponent buffer is 8 bytes and the modulus buffer is 2048 bytes in the reviewed configuration. RSA components exceeding those sizes can overwrite stack memory, causing the SSH responder to crash and potentially corrupting process state. The LDAP userCertificate;binary to SSH authorized-key lookup path requires an attacker-influenced certificate and ssh_use_certificate_keys=true. Certificate validation must succeed unless verification is explicitly disabled. The maintainer confirmed the 64-bit exponent buffer limit, the absence of prior SSSD key-size validation, and the feasibility of dynamic allocation; they consider this CVE-worthy because appropriately issued valid certificates may reach the conversion. No end-to-end arbitrary-code-execution exploit is established. Source report: PSIRTSUPT-25890, finding H-06.