Freerdp CVE-2026-23533

HIGH

Heap-based Buffer Overflow (CWE-122)

2026-01-19 security-advisories@github.com

Buffer Overflow Heap Overflow Freerdp

7.7

CVSS 4.0 · Vendor: github

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Vulnerability Assessment

Weakness

CWE

OWASP Top 10:2025

A06:2021 - Vulnerable and Outdated Components

ASVS 5.0

V15 - Secure Coding and Architecture Heap buffer bounds checking

MITRE ATT&CK

1 technique across 1 tactic: Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv5 – Jun 30, 2026

Denial of service and potential remote code execution in the FreeRDP client (all versions prior to 3.21.0) stems from a heap buffer overflow in the RDPGFX ClearCodec decoder (libfreerdp/codec/clear.c). A malicious or compromised RDP server can send crafted residual data that triggers out-of-bounds heap writes during color output on the connecting client, crashing it and potentially corrupting the heap. Publicly available exploit code exists and the GitHub advisory marks it exploitable, but the EPSS probability is low (0.15%, 35th percentile) and it is not listed in CISA KEV.

Earlier versions of this analysis (4)

v4 Jun 30, 2026 - 06:05 cvss changed CVSS 7.7

Denial-of-service and potential client-side code execution in FreeRDP prior to 3.21.0 arises from a heap buffer overflow in the RDPGFX ClearCodec decoder, where crafted residual data drives out-of-bounds writes during color output. A malicious or compromised RDP server can crash any connecting FreeRDP client and potentially corrupt the heap, with code-execution feasibility depending on allocator state. Publicly available exploit code exists; the issue is not in CISA KEV and EPSS is low (0.15%, 35th percentile), so this is a known-but-not-mass-exploited client-side flaw fixed in 3.21.0.

v3 Jun 30, 2026 - 06:04 cvss changed CVSS 7.7

Denial of service (and potential code execution) in FreeRDP RDP clients before version 3.21.0 lets a malicious or compromised RDP server crash connecting clients by sending crafted ClearCodec residual data over the RDPGFX channel, triggering a client-side heap buffer overflow during color output. The flaw affects any FreeRDP-based client that negotiates the graphics pipeline ClearCodec; publicly available exploit code exists, though it is not listed in CISA KEV and EPSS exploitation probability is low (0.15%, 35th percentile). The official CVSS 4.0 vector scores only availability impact (VA:H), but heap corruption means code execution cannot be ruled out depending on allocator behavior.

v2 Jun 30, 2026 - 06:04 cvss changed CVSS 7.7

Denial-of-service and potential client-side code execution in FreeRDP prior to 3.21.0 arises from a heap buffer overflow in the RDPGFX ClearCodec decode path, where malicious residual data forces out-of-bounds writes during color output. A malicious or compromised RDP server can crash any connecting FreeRDP-based client and potentially corrupt the heap, with code-execution risk dependent on allocator behavior. Publicly available exploit code exists, though EPSS rates real-world exploitation probability low (0.15%) and it is not listed in CISA KEV.

v1 Mar 12, 2026 - 21:54 CVSS 9.8

Additional heap overflow in FreeRDP client exploitable via malicious RDP server.

Affects your stack

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (github) PRIMARY 7.7 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P

vuln.today AI 6.5 MEDIUM

Server-to-client attack needs the victim to connect to a malicious server (UI:R); confirmed impact is a client crash (A:H) while code execution is unproven, so C:N/I:N.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

SUSE 9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Red Hat 7.6 HIGH

Primary rating from Vendor (github).

CVSS VectorVendor: github

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

None

Privileges Required

None

User Interaction

None

Vulnerable system: Confidentiality

None

Vulnerable system: Integrity

None

Vulnerable system: Availability

High

Subsequent system: Confidentiality

None

Subsequent system: Integrity

None

Subsequent system: Availability

None

Lifecycle Timeline

5

Severity Changed

Jun 30, 2026 - 03:23 NVD

CRITICAL HIGH

CVSS changed

Jun 30, 2026 - 03:23 NVD

9.8 (CRITICAL) 7.7 (HIGH)

Patch released

Apr 09, 2026 - 20:30 nvd

Patch available

PoC Detected

Jan 28, 2026 - 18:46 vuln.today

Public exploit code

CVE Published

Jan 19, 2026 - 18:16 nvd

CRITICAL 9.8

DescriptionCVE.org

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.21.0, a client-side heap buffer overflow occurs in the RDPGFX ClearCodec decode path when maliciously crafted residual data causes out-of-bounds writes during color output. A malicious server can trigger a client‑side heap buffer overflow, causing a crash (DoS) and potential heap corruption with code‑execution risk depending on allocator behavior and surrounding heap layout. Version 3.21.0 contains a patch for the issue.

Executive ViewAI

Why It Matters

FreeRDP client versions prior to 3.21.0 contain a heap buffer overflow in the ClearCodec decoder enabling remote code execution from a malicious RDP server. Organizations using FreeRDP for remote work or administration face potential compromise of client systems. Publicly available exploit code exists, though current exploitation likelihood is low.

Recommended Action

Within 24 hours: Enumerate all systems running FreeRDP and verify version numbers. Within 7 days: Upgrade FreeRDP to version 3.21.0 or later on all affected systems. Within 30 days: Confirm complete deployment of patches and update asset inventory to reflect current versions.

Business Impact: High

Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score

0.1%

Top 65% exploitable

Exploit

POC

Public exploit code exists

Data Quality

6 sources

Confidence: High

CVE.org

EPSS Vendor

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC Yes

EPSS 0.1%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

High

Priority Score

58

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +38

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Heap Overflow HIGH

A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.

Affected Products (CPE)CVE.org

cpe:2.3:a:freerdp:freerdp:*:*:*:*:*:*:*:*

More in Freerdp

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Use-after-free in FreeRDP xf_clipboard_format_equal before 3.23.0. Clipboard format comparison uses freed memory. Fifth

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Use-after-free in FreeRDP xf_SetWindowMinMaxInfo before version 3.23.0. X11 client window management triggers memory cor

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Use-after-free in FreeRDP xf_cliprdr_provide_data clipboard handling before 3.23.0. Clipboard data exchange triggers mem

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FreeRDP drive read heap overflow when server-controlled read length exceeds IRP output buffer. Fixed in 3.20.1. PoC avai

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FreeRDP client before 3.20.1 has a heap buffer overflow in AUDIN format processing. A malicious RDP server can corrupt m

CVE-2026-25955 CRITICAL Act Now POC

Use-after-free in FreeRDP xf_AppUpdateWindowFromSurface before 3.23.0. Different code path from CVE-2026-25953. PoC and

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FreeRDP is a free implementation of the Remote Desktop Protocol. Rated critical severity (CVSS 9.8), this vulnerability

CVE-2023-40574 CRITICAL Act Now POC

FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical

CVE-2023-40569 CRITICAL Act Now POC

FreeRDP is a free implementation of the Remote Desktop Protocol (RDP), released under the Apache license. Rated critical

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Vendor StatusVendor

SUSE

Severity: Critical

Product	Status
Container suse/sl-micro/6.0/baremetal-os-container:latest Container suse/sl-micro/6.0/kvm-os-container:latest Container suse/sl-micro/6.0/rt-os-container:latest	Affected
Container suse/sl-micro/6.0/base-os-container:latest Container suse/sl-micro/6.0/toolbox:latest Image SL-Micro Image SLE-Micro Image SLE-Micro-Azure Image SLE-Micro-BYOS Image SLE-Micro-BYOS-Azure Image SLE-Micro-BYOS-EC2 Image SLE-Micro-BYOS-GCE Image SLE-Micro-EC2 Image SLE-Micro-GCE	Affected
Container suse/sl-micro/6.1/baremetal-os-container:2.2.1-7.43 Container suse/sl-micro/6.1/kvm-os-container:2.2.1-5.67 Container suse/sl-micro/6.1/rt-os-container:2.2.1-5.57	Affected
Container suse/sl-micro/6.1/base-os-container:2.2.1-5.64 Image SL-Micro-Azure Image SL-Micro-BYOS-Azure Image SL-Micro-BYOS-EC2 Image SL-Micro-BYOS-GCE Image SL-Micro-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-Azure Image SUSE-Multi-Linux-Manager-Proxy-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-Azure-llc Image SUSE-Multi-Linux-Manager-Server-Azure-ltd Image SUSE-Multi-Linux-Manager-Server-BYOS-Azure Image SUSE-Multi-Linux-Manager-Server-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Server-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-EC2-llc Image SUSE-Multi-Linux-Manager-Server-EC2-ltd	Affected
SUSE Liberty Linux 8	Fixed

References

Advisories & patches

ADVISORY https://access.redhat.com/errata/RHSA-2026:2048 ADVISORY https://access.redhat.com/errata/RHSA-2026:2081 ADVISORY https://access.redhat.com/errata/RHSA-2026:2222 ADVISORY https://access.redhat.com/errata/RHSA-2026:2714 ADVISORY https://access.redhat.com/errata/RHSA-2026:2736 ADVISORY https://access.redhat.com/errata/RHSA-2026:2770 ADVISORY https://access.redhat.com/errata/RHSA-2026:2824 ADVISORY https://access.redhat.com/errata/RHSA-2026:2952 ADVISORY https://access.redhat.com/errata/RHSA-2026:3036 ADVISORY https://access.redhat.com/errata/RHSA-2026:3037 ADVISORY https://access.redhat.com/errata/RHSA-2026:3038 ADVISORY https://access.redhat.com/errata/RHSA-2026:3039 ADVISORY https://access.redhat.com/errata/RHSA-2026:3041 ADVISORY https://vuldb.com/vuln/341798 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0345/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0656/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0683/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0761/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0762/ REF https://access.redhat.com/security/cve/CVE-2026-23533 REF https://bugzilla.redhat.com/show_bug.cgi?id=2430886 REF https://github.com/FreeRDP/FreeRDP/blob/38514dfa5813aa945a86cfbcec279033f8394468/libfreerdp/codec/clear.c#L268-L281 REF https://github.com/FreeRDP/FreeRDP/blob/38514dfa5813aa945a86cfbcec279033f8394468/libfreerdp/codec/clear.c#L336 REF https://github.com/FreeRDP/FreeRDP/releases/tag/3.21.0 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-23533.json

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