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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

FreeRDP clients before 3.21.0 can be crashed by a malicious RDP server using crafted graphics updates. The bug is client-side, so the main risk is users or automated systems connecting to hostile or compromised RDP servers. Heap corruption creates code-execution concern, but the provided sources do not confirm exploitation in the wild.

Executive priority

Treat as a high-priority client update for environments where FreeRDP is used to reach third-party, internet-adjacent, or less-trusted RDP systems. Prioritize jump hosts and shared administrative workstations because compromise or disruption there can affect broader operations.

Technical view

The flaw is a CWE-122 heap-buffer-overflow in ClearCodec clear_decompress. When glyphData is present, FreeRDP calls freerdp_image_copy_no_overlap without validating the destination rectangle, allowing out-of-bounds read/write through crafted RDPGFX surface updates. Version 3.21.0 contains the fix.

Likely exposure

Exposure is most likely on systems running FreeRDP or software linked against libfreerdp below 3.21.0, especially Linux desktops, jump hosts, thin clients, or automation that connects to external RDP servers. Downstream vendor packages may be fixed through backports rather than showing version 3.21.0.

Exploitation context

The provided bundle marks KEV as false and does not cite confirmed active exploitation. Attack requires a malicious or compromised RDP server capable of sending crafted RDPGFX surface updates to a vulnerable client. Expected impact is denial of service, with possible heap-corruption risk depending on runtime conditions.

Researcher notes

The strongest evidence is the FreeRDP advisory and patched release. The CVSS 4.0 score is 7.7 with network attack vector and high availability impact. Code-execution risk is plausible from heap corruption, but the source bundle does not prove reliable exploitation or active attacks.

Mitigation direction

  • Upgrade FreeRDP to 3.21.0 or a vendor-fixed package.
  • Apply applicable Red Hat errata where Red Hat packages are in use.
  • Restrict FreeRDP connections to trusted RDP servers until patched.
  • Inventory bundled or statically linked libfreerdp copies.
  • Monitor vendor advisories for distribution-specific backports.

Validation and detection

  • Confirm FreeRDP or libfreerdp is 3.21.0 or vendor-fixed.
  • Map installed packages to the Red Hat CVE page and applicable RHSAs.
  • Check applications that embed FreeRDP for linked library versions.
  • Review telemetry for connections to untrusted or unusual RDP servers.
  • Retest representative RDP workflows after updating.
Prepared
Confidence
high
Sources
10

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

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-23531 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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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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