Security readout for executives and security teams
Plain-English summary
A malicious RDP server can exploit vulnerable FreeRDP clients when a user connects. The flaw can corrupt memory, potentially crashing the client or allowing attacker-controlled code execution with the client process’s privileges. FreeRDP versions before 3.26.0 are affected.
Executive priority
Treat as a high-priority client-side update, especially for administrators, support teams, and users connecting to third-party RDP servers. Patch promptly because successful exploitation could compromise confidentiality, integrity, and availability, although active exploitation is not established by the supplied evidence.
Technical view
gdi_CacheToSurface clamps rectangle coordinates to UINT16_MAX during validation but performs copying with unclamped cache-entry dimensions. This mismatch permits large out-of-bounds heap writes. The CVSS 3.1 score is 8.8: exploitation is network-accessible, low complexity, requires no privileges, and requires user interaction.
Likely exposure
Exposure centers on systems running FreeRDP before 3.26.0 that connect to attacker-controlled or compromised RDP servers. Risk depends on whether users or automated workflows initiate such connections. The supplied sources do not identify additional affected products.
Exploitation context
The attack originates from a malicious RDP server and is triggered when a vulnerable client connects. Potential outcomes include client crashes and remote code execution. CISA KEV status is false, and the supplied evidence does not establish active exploitation or public weaponization.
Researcher notes
The upstream patch is commit d7508ebcd82842a691ae4941e5104d14240a89ae, associated with pull request 12713. Validation should focus on consistency between rectangle validation and copy dimensions. The supplied bundle does not provide evidence of observed attacks, reliable exploitation, or impact beyond FreeRDP.
Mitigation direction
- Upgrade FreeRDP to version 3.26.0 or later.
- Apply applicable operating-system vendor updates or Red Hat errata.
- Prioritize clients permitted to connect to untrusted RDP servers.
- Restrict RDP client connections to approved servers until updates are complete.
Validation and detection
- Inventory installed FreeRDP versions and identify releases earlier than 3.26.0.
- Confirm distribution packages include the vendor patch or applicable security erratum.
- Verify updated clients report FreeRDP 3.26.0 or a patched vendor build.
- Review whether vulnerable clients can connect to untrusted or externally controlled RDP servers.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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-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.
Open ATT&CK lookupCWE-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.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-40033 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- 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
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.
SSVC decision data
CVSS vector scores
3 official scoresWe 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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9redhat-SADPCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N——VulnCheckVulnerability scoring details
Base CVSS 4.0 score
8.6HighVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Made public.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-05-26T15:01:26.044Z: Reported to Red Hat.
- 2026-05-26T14:08:47.535Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-p6r2-4hgm-m6ffCVE reference, VulnCheck · vendor-advisory
- https://github.com/FreeRDP/FreeRDP/pull/12713CVE reference, VulnCheck · issue-tracking
- https://github.com/FreeRDP/FreeRDP/commit/d7508ebcd82842a691ae4941e5104d14240a89aeCVE reference, VulnCheck · patch
- https://www.vulncheck.com/advisories/freerdp-heap-buffer-overflow-in-gdi-cachetosurface-via-rectangle-validation-bypassCVE reference, VulnCheck · third-party-advisory
- https://access.redhat.com/security/cve/CVE-2026-40033CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2481473CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40033.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:46393CVE reference, redhat-SADP · vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/errata/RHSA-2026:36203CVE reference, redhat-SADP · vendor-advisory, x_refsource_REDHAT
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
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.
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.