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CVE Record

CVE-2026-26955: FreeRDP has Out-of-bounds Write

FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.23.0, a malicious RDP server can trigger a heap buffer overflow in FreeRDP clients using the GDI surface pipeline (e.g., `xfreerdp`) by sending an RDPGFX ClearCodec surface command with an out-of-bounds destination rectangle. The `gdi_SurfaceCommand_ClearCodec()` handler does not call `is_within_surface()` to validate the command rectangle against the destination surface dimensions, allowing attacker-controlled `cmd->left`/`cmd->top` (and subcodec rectangle offsets) to reach image copy routines that write into `surface->data` without bounds enforcement. The OOB write corrupts an adjacent `gdiGfxSurface` struct's `codecs*` pointer with attacker-controlled pixel data, and corruption of `codecs*` is sufficient to reach an indirect function pointer call (`NSC_CONTEXT.decode` at `nsc.c:500`) on a subsequent codec command — full instruction pointer (RIP) control demonstrated in exploitability harness. Users should upgrade to version 3.23.0 to receive a patch.

HighCVSS 8.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A malicious or compromised RDP server could attack vulnerable FreeRDP clients when a user connects. The bug can corrupt client memory and may allow code execution with the user's privileges. This is client-side risk, not exposure of an RDP server port.

Executive priority

Prioritize patching user workstations, admin systems, jump boxes, and support tooling that use FreeRDP. The business risk is compromise of the connecting client after interaction with a malicious or compromised RDP server.

Technical view

FreeRDP before 3.23.0 lacks destination surface bounds validation in gdi_SurfaceCommand_ClearCodec(). An attacker-controlled RDPGFX ClearCodec surface command can cause heap out-of-bounds writes in the GDI surface pipeline, corrupting adjacent structures and reaching an indirect codec function call in demonstrated exploitability testing.

Likely exposure

Systems running FreeRDP clients earlier than 3.23.0, including xfreerdp and distribution packages, are most relevant. Exposure is higher where users connect to untrusted, third-party, or potentially compromised RDP servers.

Exploitation context

The source bundle reports no KEV listing and provides no evidence of active exploitation. It does describe a malicious-server attack path and demonstrated instruction pointer control in a harness, so exploitation potential is credible even if field exploitation is unconfirmed.

Researcher notes

The key missing check is is_within_surface() in the ClearCodec handler. Focus assessment on FreeRDP GDI surface pipeline client builds before 3.23.0. Treat public exploit status as unproven unless a cited advisory changes that.

Mitigation direction

  • Upgrade FreeRDP to version 3.23.0 or a vendor-fixed package.
  • Apply relevant Red Hat or distribution errata where FreeRDP is packaged.
  • Avoid connecting vulnerable clients to untrusted RDP servers until patched.
  • Inventory bundled or statically shipped FreeRDP clients in tools and images.
  • Follow vendor guidance for any platform-specific compensating controls.

Validation and detection

  • Check installed FreeRDP and xfreerdp versions are 3.23.0 or later.
  • Confirm package changelogs or advisories reference CVE-2026-26955.
  • Identify systems using FreeRDP clients to access external RDP servers.
  • Verify endpoint images and remote-support tools do not bundle vulnerable FreeRDP.
  • Review vendor errata applicability for each affected operating system.
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-787: 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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cwe · low confidence lookup

CWE-805: 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-2026-26955 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
8.8 (3.1)
Known Exploited
No
Published

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

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: noTechnical Impact: total

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
8.8CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9GitHub_M
8.8CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

8.8High
CVSS 3.1 vector shape for CVE-2026-26955Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
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: Arbitrary code execution via heap buffer overflow in GDI surface pipeline
other:Red Hat severity ratingcvssV3_1
  • 2026-02-26T21:03:46.682Z: Reported to Red Hat.
  • 2026-02-25T20:47:14.660Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
FreeRDPFreeRDP< 3.23.0Listed
Weakness

CWE details

CWE-787CWE-805

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

CWE-787 · source CWE mapping

Out-of-bounds Write

Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-805 · source CWE mapping

Buffer Access with Incorrect Length Value

Buffer Access with Incorrect Length Value represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs