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CVE Record

CVE-2026-23531: FreeRDP has heap-buffer-overflow in clear_decompress

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.

HighCVSS 7.7Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A malicious RDP server can crash or potentially corrupt memory in vulnerable FreeRDP clients before 3.21.0. The issue is client-side, so exposure is highest where users or automation connect to untrusted or compromised RDP servers. A patch is identified in FreeRDP 3.21.0.

Executive priority

Treat this as a high-priority client-side patching issue, especially for administrator and support systems. The known patch path is clear, but the source bundle does not prove active exploitation. Reduce exposure by patching and constraining connections to trusted RDP servers.

Technical view

In ClearCodec clear_decompress, when glyphData is present, the destination rectangle is not validated before freerdp_image_copy_no_overlap. Crafted RDPGFX surface updates can cause out-of-bounds read/write and heap-buffer-overflow. Documented impact is client crash, with potential heap corruption and code-execution risk dependent on allocator behavior and heap layout.

Likely exposure

Organizations using FreeRDP clients or libraries earlier than 3.21.0 are exposed. Risk is more relevant for endpoints, admin workstations, jump-host workflows, support tooling, or automation that initiates RDP connections to servers outside strict trust boundaries.

Exploitation context

The source bundle describes a malicious server triggering the flaw through crafted RDPGFX surface updates. CISA KEV status is false in the provided data, and the bundle does not cite confirmed active exploitation in the wild.

Researcher notes

The key condition is glyphData handling in ClearCodec clear_decompress before a copy into the destination surface. Analysis should focus on whether deployed builds include the vulnerable code path and whether downstream vendors have backported the 3.21.0 fix.

Mitigation direction

  • Upgrade FreeRDP to version 3.21.0 or later.
  • Apply relevant downstream vendor updates, including Red Hat errata where applicable.
  • Prioritize clients that connect to third-party, internet-facing, or less-trusted RDP servers.
  • Limit FreeRDP use to trusted RDP servers until patched.
  • Monitor FreeRDP and distribution advisories for additional guidance.

Validation and detection

  • Inventory systems and applications that include FreeRDP client components.
  • Confirm installed FreeRDP versions are 3.21.0 or later.
  • Check distribution package advisories for fixed package availability and applicability.
  • Verify Red Hat errata status for affected Red Hat-managed environments.
  • Review crash telemetry for FreeRDP client failures after RDPGFX sessions.
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-2026-23531 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-2026-23531Attack 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 via crafted RDPGFX surface updates leads to denial of service and potential code execution.
other:Red Hat severity ratingcvssV3_1
  • 2026-01-19T18:01:53.381Z: Reported to Red Hat.
  • 2026-01-19T17:01:01.380Z: 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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