CVE-2026-55191Public exploitNetwork attack vector

Heap overwrite via wrapped AVC444 allocation

Published Aug 19, 2026 · Updated Aug 19, 2026

Heap overflow in FreeRDP before 3.27.0 allows remote attackers to crash a client or execute code via crafted AVC444 RDPGFX updates. In libfreerdp/codec/h264.c, avc444_ensure_buffer() multiplies piDstStride by padDstHeight in 32-bit arithmetic, accepts wrapped nonzero sizes, and allocates an undersized YUV444 buffer before YUV420CombineToYUV444() writes with the true stride and rectangle dimensions. Reachability requires a FreeRDP client session that negotiates RDPGFX AVC444 with an H.264 decoder backend; server-only deployments and builds without H.264 support are not affected.

CVSS severity8.8
High
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Heap overflow in FreeRDP before 3.27.0 allows remote attackers to crash a client or execute code via crafted AVC444 RDPGFX updates. In libfreerdp/codec/h264.c, avc444_ensure_buffer() multiplies piDstStride by padDstHeight in 32-bit arithmetic, accepts wrapped nonzero sizes, and allocates an undersized YUV444 buffer before YUV420CombineToYUV444() writes with the true stride and rectangle dimensions. Reachability requires a FreeRDP client session that negotiates RDPGFX AVC444 with an H.264 decoder backend; server-only deployments and builds without H.264 support are not affected.

The record

CVE
CVE-2026-55191
Published
Aug 19, 2026
Updated
Aug 19, 2026
Vendor
FreeRDP
Product
FreeRDP
Classifications
CWE-122, CWE-190, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 3.27.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

FreeRDP · FreeRDPversion=< 3.27.0

Published CVSS scores

8.8Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-122Heap-based Buffer Overflow
CWE-190Integer Overflow or Wraparound
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo