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CVE Record

CVE-2026-23533: FreeRDP has heap-buffer-overflow in clear_decompress_residual_data

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.

HighCVSS 7.7Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is a client-side FreeRDP flaw. A malicious RDP server can send crafted graphics data that overflows heap memory in vulnerable FreeRDP clients before 3.21.0. The most clearly supported impact is client crash; the source also notes possible heap corruption and code-execution risk depending on runtime conditions.

Executive priority

Treat as a high-priority client update where FreeRDP is used for administration, remote access, or automation. Prioritize environments that connect to external or less trusted RDP servers. Current sources support patching urgency but not confirmed active exploitation.

Technical view

CVE-2026-23533 is a CWE-122 heap buffer overflow in FreeRDP's RDPGFX ClearCodec decode path, specifically residual data handling in clear_decompress_residual_data. Malicious residual data can cause out-of-bounds writes during color output. Affected versions are FreeRDP before 3.21.0. CVSS v4.0 is 7.7 High.

Likely exposure

Exposure is most likely on systems running FreeRDP clients or software that embeds vulnerable libfreerdp versions before 3.21.0, especially where users or automation connect to untrusted, compromised, or attacker-controlled RDP servers.

Exploitation context

The provided bundle does not show CISA KEV listing or active exploitation. The scenario is server-to-client: a malicious RDP server triggers memory corruption in the connecting FreeRDP client through crafted RDPGFX ClearCodec data.

Researcher notes

Focus review on the RDPGFX ClearCodec residual-data decode path and bounds handling around color output. The public evidence supports DoS and heap-corruption risk; reliable code execution is described as conditional, not demonstrated in the provided bundle.

Mitigation direction

  • Upgrade FreeRDP to version 3.21.0 or later.
  • Apply applicable vendor packages, including relevant Red Hat advisories where used.
  • Avoid connecting vulnerable FreeRDP clients to untrusted RDP servers until updated.
  • Check vendor guidance for supported backports and distribution-specific fixed versions.

Validation and detection

  • Inventory endpoints and servers for FreeRDP and libfreerdp versions below 3.21.0.
  • Confirm package status against FreeRDP 3.21.0 release notes or vendor errata.
  • Identify workflows that connect FreeRDP clients to third-party or untrusted RDP servers.
  • Review recent FreeRDP client crash telemetry after RDP connections.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-122: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-23533 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.7 (4.0)
Known Exploited
No
Published

Vector: 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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
20Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.7CVSS 4.0HighCVSS: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——GitHub_M
7.6CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H2.84.7redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

7.7High
CVSS 4.0 vector shape for CVE-2026-23533Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPfreerdp: FreeRDP: Heap buffer overflow leads to denial of service and potential code execution
other:Red Hat severity ratingcvssV3_1
  • 2026-01-19T18:01:48.107Z: Reported to Red Hat.
  • 2026-01-19T17:07:18.283Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
FreeRDPFreeRDP< 3.21.0Listed
Weakness

CWE details

CWE-122

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-122 · source CWE mapping

Heap-based Buffer Overflow

Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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