CVE-2026-111880
Description
A flaw was found in FreeRDP. An out-of-bounds write vulnerability in the server-side NT LAN Manager (NTLM) authentication path can result in a Denial of Service (DoS). When processing authentication messages with hash callbacks enabled, FreeRDP fails to properly validate the Message Integrity Check (MIC) offset. A remote, unauthenticated attacker can exploit this issue by sending a specially crafted authentication message, corrupting heap memory and causing the server to crash.
Statement
This issue is reachable only on FreeRDP server or proxy peers that configure the non-default SspiNtlmHashCallback NTLM hash callback, which is reflected as Attack Complexity: High. An unauthenticated network attacker can cause a fixed 16-byte out-of-bounds heap write, so Integrity and Availability are High; Confidentiality is None. Red Hat rates this Important. Platform safeguards such as ASLR, NX, FORTIFY_SOURCE, and glibc allocator hardening may impede reliable code execution, but they do not prevent the out-of-bounds write or process crash, so the base metrics are unchanged.
Mitigation
Do not expose FreeRDP server or proxy endpoints that use SspiNtlmHashCallback to untrusted networks; restrict access with a host firewall and network segmentation. If the NTLM hash callback is not required, leave it unset so the vulnerable MIC path is not entered.
--- CME Mitigation Guidance (2026-10-20) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.
The highest-value action is to enforce bounds validation on Message Integrity Check (MIC) offsets within the authenticate message buffer before writing in ntlm_computeMicValue: upgrade to FreeRDP 3.32.0 (or the fixed Freerdp builds), which validate that the MIC offset is within the authenticate message buffer bounds before writing bytes, closing crafted NTLM AUTHENTICATE_MESSAGE with backward session-key offset and out-of-bounds MIC offset. Until patched, this is a concern on FreeRDP server and proxy instances configured with the non-default SspiNtlmHashCallback setting, so leave SspiNtlmHashCallback unset if NTLM hash callbacks are not required, and restrict network access to FreeRDP endpoints from untrusted networks using firewalls and network segmentation. As a compensating measure, configure systemd service restart and watchdog settings to automatically restart FreeRDP upon process crashes and mitigate prolonged denial of service, require pre-authentication through a zero-trust gateway or identity-aware proxy before clients can reach the FreeRDP NTLM authentication handler, and restrict FreeRDP port access with host firewalls using firewalld or nftables to isolate the service from untrusted networks. These controls limit blast radius and contain exploitation, but they do not fix the underlying heap out-of-bounds write defect — apply the upstream patch to fully remediate.
Highest-impact CME: CME-1311 Input Size and Quantity Bounds Enforcement (high)
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | N/A | 7.4 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
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