CVE-2023-40181Public exploitNetwork attack vector

Client crash via ZGFX bit-count underflow

Published Aug 31, 2023 · Updated Nov 3, 2025

Out-of-bounds read in FreeRDP before 2.11.0 and 3.0.0-beta1 through 3.0.0-beta2 allows remote attackers to crash clients. In zgfx_decompress_segment, the final input byte is subtracted from the available bit count without validating the segment length, so an underflow makes the CopyMemory bounds check accept a count beyond the packet. Only FreeRDP-based clients that decode attacker-controlled compressed GFX segments are exposed; proxy deployments do not perform image decoding.

CVSS severity5.3
Medium
EPSS probability1.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in FreeRDP before 2.11.0 and 3.0.0-beta1 through 3.0.0-beta2 allows remote attackers to crash clients. In zgfx_decompress_segment, the final input byte is subtracted from the available bit count without validating the segment length, so an underflow makes the CopyMemory bounds check accept a count beyond the packet. Only FreeRDP-based clients that decode attacker-controlled compressed GFX segments are exposed; proxy deployments do not perform image decoding.

The record

CVE
CVE-2023-40181
Published
Aug 31, 2023
Updated
Nov 3, 2025
Vendor
FreeRDP
Product
FreeRDP
Classifications
CWE-191, CWE-125, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 31, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.11.0
  2. Affected versionversion=>= 3.0.0-beta1, < 3.0.0-beta3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

FreeRDP · FreeRDPversion=< 2.11.0; version=>= 3.0.0-beta1, < 3.0.0-beta3

Published CVSS scores

9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)
CWE-125Out-of-bounds Read
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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