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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

FreeRDP clients before 3.21.0 can be crashed by a malicious RDP server and may suffer memory corruption. This matters most where FreeRDP is used for remote access, support tooling, automation, or embedded RDP workflows. The source bundle identifies a patch in FreeRDP 3.21.0.

Executive priority

Treat this as high priority for environments using FreeRDP clients. There is no provided evidence of active exploitation, but the bug is network-triggerable by a malicious server and can crash clients with possible memory-corruption consequences. Patch through FreeRDP 3.21.0 or vendor updates.

Technical view

CVE-2026-23533 is a client-side heap buffer overflow in FreeRDP's RDPGFX ClearCodec decode path, specifically clear_decompress_residual_data. Crafted residual data can cause out-of-bounds writes during color output. Reported impact is crash, denial of service, and potential code-execution risk depending on heap layout and allocator behavior.

Likely exposure

Exposure is likely where systems run FreeRDP client components older than 3.21.0, including Linux distributions or products bundling FreeRDP. The provided Red Hat advisories indicate downstream packaging impact, but the bundle does not enumerate every affected package or platform.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of active exploitation. The attack scenario is a malicious server triggering the vulnerable client-side decoder. The CVSS vector indicates network reachability, low complexity, no privileges, and high availability impact.

Researcher notes

Key evidence is the FreeRDP advisory, source references in libfreerdp/codec/clear.c, and the 3.21.0 release. The bundle does not provide exploit proof, weaponized samples, or detailed fixed-package mapping beyond Red Hat advisory references. Avoid assuming affected products beyond FreeRDP and vendor packages that declare impact.

Mitigation direction

  • Upgrade FreeRDP to version 3.21.0 or a vendor-fixed package.
  • Apply relevant Red Hat errata where Red Hat packages are used.
  • Avoid connecting vulnerable FreeRDP clients to untrusted RDP servers.
  • Check vendor guidance for platform-specific backports and package names.
  • Prioritize systems that initiate RDP sessions to third-party or unmanaged hosts.

Validation and detection

  • Inventory FreeRDP client versions and identify anything below 3.21.0.
  • Check OS package advisories against the listed Red Hat RHSA references.
  • Confirm patched builds include the FreeRDP 3.21.0 fix or vendor backport.
  • Review remote-access workflows for FreeRDP use in automation or support tools.
  • Verify no vulnerable client package remains in gold images or containers.
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

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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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