EUVD-2026-56135
GHSA-9q6x-42cw-m8jx
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable pre-authentication; EC field misuse yields OOB heap read and write, covering confidentiality, integrity, and availability impacts.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3DescriptionCVE.org
FreeRDP before 3.30.0 contains an out-of-bounds vulnerability in kerberos_DecryptMessage() (winpr/libwinpr/sspi/Kerberos/kerberos.c). The 16-bit EC (extra count) field of a peer-supplied GSS Wrap token (RFC 4121) is used directly in pointer arithmetic to locate the encrypted regions without being bounds-checked, while only RRC and the total buffer length are validated. A malicious peer (server or client) can supply a large EC value (up to 0xFFFF) during CredSSP/NLA authentication, moving the decrypt operation's base pointers past the end of the ~60-byte token buffer. Because the AES-CTS-HMAC enctypes decrypt in place before the HMAC integrity check, this results in an out-of-bounds read and in-place out-of-bounds write, potentially leading to information disclosure, memory corruption, or denial of service.
AnalysisAI
Heap-based out-of-bounds read and write in FreeRDP before 3.30.0 can be triggered by a malicious peer during CredSSP/NLA Kerberos authentication, allowing information disclosure, heap memory corruption, or denial of service. The flaw exists in kerberos_DecryptMessage() where the peer-supplied 16-bit EC field of a GSS Wrap token is used directly in pointer arithmetic without bounds validation, enabling any RDP peer - rogue server or malicious client - to shift decrypt pointers up to 65535 bytes past the end of a ~60-byte token buffer. No public exploit code has been identified at time of analysis, and the vulnerability is not listed in CISA KEV.
Technical ContextAI
FreeRDP is an open-source Remote Desktop Protocol implementation widely deployed as an RDP client and library on Linux, embedded in remote desktop tooling and thin-client environments. The vulnerability resides in winpr/libwinpr/sspi/Kerberos/kerberos.c within kerberos_DecryptMessage(), which processes GSS Wrap tokens as defined by RFC 4121. The GSS Wrap token header includes a 16-bit EC (Extra Count) field that indicates the number of filler bytes appended during encryption, and a separate RRC (Right Rotation Count) field. The code validates RRC and total buffer length but applies the peer-supplied EC value directly in pointer arithmetic to locate the encrypted payload region without range-checking it against the actual buffer. Because AES-CTS-HMAC enctypes decrypt in-place prior to HMAC integrity verification, a crafted EC value up to 0xFFFF causes the decrypt base pointer to land well past the end of the heap-allocated ~60-byte token buffer, producing a heap-based out-of-bounds read and write before any integrity check can abort the operation. CWE-122 (Heap-based Buffer Overflow) describes this root cause precisely. Affected product per CPE: cpe:2.3:a:freerdp:freerdp:*:*:*:*:*:*:*:*.
RemediationAI
Upgrade FreeRDP to version 3.30.0 or later, which resolves the missing EC field bounds check per the vendor advisory at https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-vv64-95pc-vj9v. This is the only confirmed fix; no patch backport to older stable branches has been identified from available data. If an immediate upgrade is not feasible, disable Kerberos-based CredSSP/NLA authentication in RDP configuration and fall back to NTLM-based NLA or certificate-only authentication, accepting the trade-off that NTLM may offer weaker authentication security in some environments. FreeRDP clients can additionally be restricted via policy to connect only to trusted, verified servers, reducing exposure to malicious-server exploitation. Network controls that limit RDP traffic (TCP 3389) to known authorized endpoints reduce the attack surface for both client- and server-side scenarios. Additional VulnCheck advisory context is available at https://www.vulncheck.com/advisories/freerdp-before-out-of-bounds-read-via-kerberos-gss-wrap-token-ec.
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FreeRDP is a free implementation of the Remote Desktop Protocol. Rated critical severity (CVSS 9.8), this vulnerability
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical
Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
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