Bug 2572592 (CVE-2026-127101)

Summary: CVE-2026-127101 sssd: sssd: NULL pointer dereference in PAM responder when protocol version negotiation is skipped
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
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Hardware: All   
OS: Linux   
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A flaw was found in SSSD's PAM responder. A local attacker can send an authentication request without first negotiating the client protocol version. The responder dereferences a NULL protocol-version pointer and crashes, disrupting SSSD-backed authentication. Repeated crafted requests can sustain the denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2572658    
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Description OSIDB Bzimport 2026-11-12 15:04:23 UTC 
A flaw was found in SSSD. In src/responder/pam/pamsrv_cmd.c, pam_forwarder_parse_data() dereferences prctx->cli_protocol_version->version without first checking whether the client negotiated a protocol version with SSS_GET_VERSION. The pointer is initialized to NULL at connection setup and is only populated during version negotiation. A local user able to connect to the PAM responder socket can send a PAM command before SSS_GET_VERSION, causing a NULL pointer dereference and terminating sssd_pam. Repeated requests can sustain denial of SSSD-backed authentication. The review describes a header-only 16-byte request reaching the vulnerable switch. The maintainer confirmed that recent versions do not initialize a non-NULL default and that rejecting requests when cli_protocol_version is NULL is a valid fix. A possible similar issue in sudosrv_cmd() was noted by the maintainer but is not established as part of this flaw. This is distinct from CVE-2026-90995 (missing service item in get_domain_request_type()) and CVE-2026-104042 (zero-length authentication token out-of-bounds read). Source: PSIRTSUPT-25890, finding H-09; security review dated 2026-10-21 and maintainer assessment.