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FreerdpApplication

CVE-2026-23531

CRITICAL · 9.8 CVSS v3.1 Published 2026-01-19
Fix available
A fix is available. Upgrade to 3.21.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.21.0, in ClearCodec, when `glyphData` is present, `clear_decompress` calls `freerdp_image_copy_no_overlap` without validating the destination rectangle, allowing an out-of-bounds read/write via crafted RDPGFX surface updates. 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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

FreeRDP versions prior to 3.21.0 contain a heap buffer overflow in ClearCodec's clear_decompress function. When glyphData is present, the function calls freerdp_image_copy_no_overlap without validating the destination rectangle, allowing a malicious RDP server to trigger out-of-bounds read/write via crafted RDPGFX surface updates, leading to potential code execution.

MitigationUpgrade FreeRDP to version 3.21.0 or later. Until then, limit RDP connections to trusted servers only, as this is a client-side vulnerability exploitable by malicious servers.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FreerdpApplication
Affected:< 3.21.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify FreeRDP client version
    Run `freerdp-version` or `xfreerdp -version` to obtain the installed FreeRDP client version. Alternatively, check the package manager (dpkg -l freerdp or rpm -qi freerdp) for the installed version.
    Affected if The installed version is less than 3.21.0 (e.g., 3.0.0, 3.16.0, 2.x series)
  2. Verify ClearCodec module presence
    Check for the presence of the ClearCodec plugin in the FreeRDP installation directory, typically found in /usr/lib/freerdp/ or /usr/lib/x86_64-linux-gnu/freerdp/ as libclearcodec.so or similar.
    Affected if The ClearCodec library file exists in the FreeRDP plugins directory on a vulnerable version
  3. Confirm RDP session uses ClearCodec decoding
    Inspect RDP connection logs or traffic captures to determine if the server advertises and the client uses the ClearCodec (CLRCAP) codec for bitmap decompression during the session.
    Affected if The RDP session successfully negotiates and uses ClearCodec for remote graphics decoding
  4. Check for glyphData in surface updates
    Enable debug logging in FreeRDP (via /log:debug) and examine logs for RDPGFX surface updates containing glyphData fields being processed by the clear_decompress function.
    Affected if The client processes RDPGFX surface updates with glyphData present on a vulnerable version

You are affected if your FreeRDP client version is below 3.21.0 AND the ClearCodec decoder is present and used during RDP sessions, as the heap buffer overflow requires glyphData in crafted surface updates to trigger.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.21.0 or later
Fixed in 3.21.0
Interim mitigation

Upgrade FreeRDP to version 3.21.0 or later. Until then, limit RDP connections to trusted servers only, as this is a client-side vulnerability exploitable by malicious servers.

Recommended fix High confidence

3.21.0

  1. Identify the current FreeRDP version installed in your environment
  2. Upgrade FreeRDP to version 3.21.0 or later
  3. Verify the upgrade was successful by checking the installed version

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Freerdp Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,160
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.

Scan for this in your stack

Free · runs locally
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-23531 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data