Medium [CVE-2026-18663] pre-authentication double-free in get_ldapmessage_controls_ext via critical Session Tracking control
This medium-severity Red Hat Linux advisory covers CVE-2026-18663 affecting Red Hat Directory Server 13, Red Hat Enterprise Linux 10, Red Hat package: 389-ds-base.
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Summary
A flaw was found in 389-ds-base. The get_ldapmessage_controls_ext() function frees the parsed controls array on the Session Tracking critical-control rejection path without clearing the SLAPI_REQCONTROLS pblock slot.
Operation teardown then frees the same pointer again, causing a double-free. An unauthenticated remote attacker can trigger this with a single BIND request carrying a critical Session Tracking control, resulting in heap corruption and potential denial of service.
Red Hat rates this issue as Moderate severity primarily because the exploitation requires sending an unauthenticated BIND request with a critical Session Tracking control, but on RHEL 10 and RHDS 13 the ns-slapd process uses jemalloc, which absorbs the double-free without crashing.
Live testing confirmed the error path is hit but the server continues running. Impact is limited to heap corruption; no information disclosure or privilege escalation has been demonstrated.
Reliable denial of service only occurs on builds using the glibc allocator (upstream/Fedora), not on RHEL product builds. Other versions are not affected as they lack the Session Tracking control feature.
Weakness: CWE-415. Affected Red Hat products: Red Hat Directory Server 13; Red Hat Enterprise Linux 10.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: 389-ds-base.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- On builds that include upstream Issue 7389 (committed 2026-04-09, present in 389-ds-base-3.2 branch), administrators can add the Session Tracking control OID (1.3.6.1.4.1.21008.108.63.1) to the ds-ignored-control-criticality configuration attribute. This causes the server to ignore the criticality flag on this control, preventing the vulnerable rejection path from being reached. Additionally, network-level restriction of access to the LDAP port (389/636) to trusted clients reduces exposure.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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