Bug 2533698 (CVE-2026-91926)

Summary:	CVE-2026-91926 gss-ntlmssp: gss-ntlmssp: memory leak in ntlm_decode_target_info via duplicated AV_PAIR entries in NTLM CHALLENGE
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in gss-ntlmssp. A memory leak occurs in the NTLM target-info parser when a crafted NTLM CHALLENGE message contains duplicated string-valued AV_PAIR entries. The parser allocates memory for each string value but does not free the previous allocation when the same AV_PAIR type appears more than once, leaking the earlier allocation. A malicious or man-in-the-middle server can exploit this to cause gradual memory exhaustion on the client during NTLM authentication, leading to a denial of service.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
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Description OSIDB Bzimport 2026-09-15 10:57:00 UTC

gss-ntlmssp (gssapi/gss-ntlmssp) contains a memory leak in the NTLM CHALLENGE target-info parsing on the client (initiator) path. The function ntlm_decode_av_pair_u16l_str() in src/ntlm.c (line 444) allocates a buffer via malloc and assigns it to *str (line 464) without freeing any previous value. The caller ntlm_decode_target_info() (line 637) iterates over AV_PAIRs in a while loop and decodes each string-valued AV_PAIR (MSV_AV_NB_COMPUTER_NAME, MSV_AV_NB_DOMAIN_NAME, MSV_AV_DNS_COMPUTER_NAME, MSV_AV_DNS_DOMAIN_NAME, MSV_AV_DNS_TREE_NAME, MSV_AV_TARGET_NAME) into local variables. If a CHALLENGE message contains a duplicated string-valued AV_PAIR ID, the second call overwrites the local pointer without freeing the first allocation. The done: cleanup only frees the last value held. The acceptor path (gss_sec_ctx.c:843) passes NULL for all six string out-parameters, so the leak does not fire server-side. The initiator path is reachable via ntlm_process_target_info() (src/ntlm.c:765), called from gssntlm_cli_auth() in src/gss_auth.c:85, which passes all six string parameters non-NULL. The unguarded allocation predates the February 2023 security batch (GHSL-2023-011/012/013) and was not caught because oss-fuzz drives the acceptor entry point which never runs the string decode. By inspection, all released versions are affected. Reported by Chase Bevan-Thomas (cbev0x), independent security researcher. No upstream fix available at time of report. PSIRT Ticket: PSIRTSUPT-23614. Verified via static analysis in Kaiden sandbox.