CVE-2026-64620
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFreeRDP before 3.28.0 (affected <=3.27.1) contains a heap-based buffer overflow in crypto_rsa_common() (libfreerdp/crypto/crypto.c). The function writes the modular-exponentiation result into the caller's output buffer via BN_bn2bin() and only afterward checks output_length > out_length, so out-of-bounds bytes are written before the bounds check. On the server side, when a client selects RDP Standard Security, the encrypted client random is decrypted into a fixed 32-byte buffer. Because the server publishes its RSA public key, an unauthenticated attacker can forge a ciphertext whose decrypted value is up to the full modulus length (e.g. 256 bytes for RSA-2048), overflowing the 32-byte heap buffer by up to ~224 attacker-controlled bytes pre-authentication, resulting in denial of service.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceHeap-based buffer overflow in FreeRDP's crypto_rsa_common() function allows unauthenticated attackers to overflow a 32-byte heap buffer by up to ~224 bytes via a crafted RSA ciphertext. The function writes the RSA decryption result via BN_bn2bin() before performing the output_length bounds check, enabling pre-authentication overflow on RDP servers using Standard Security mode.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 3.28.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify FreeRDP installation and versionRun 'freerdp-version' or check package manager (dpkg -l freerdp, rpm -qi freerdp). For servers, check the FreeRDP server component version if running freerdp-server service.Affected if FreeRDP version is found and is less than 3.28.0
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Determine if RDP Standard Security is in useInspect RDP connection configuration or server settings. Standard Security is the default RDP security mode. Check /etc/freerdp/ settings, .rdp files, or connection logs for SecurityMode=Standard or absence of NLA/TLS security negotiation.Affected if RDP connections use Standard Security mode (default) rather than NLA or TLS authentication
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Check for active FreeRDP servicesIdentify if freerdp-server, xrdp, or any FreeRDP-based RDP server process is running using 'ps aux | grep -i freerdp' or 'systemctl list-units | grep -i rdp'.Affected if FreeRDP-based RDP server or client is actively running with version < 3.28.0 using Standard Security
Environment is affected if FreeRDP version is below 3.28.0 and RDP Standard Security mode (the default) is in use for client or server connections.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.28.0
Upgrade FreeRDP to version 3.28.0 or later to obtain the patched version with proper bounds checking before the BN_bn2bin() write operation.
FreeRDP 3.28.0
- Check the current FreeRDP version installed on the system using package manager or freerdp-version command
- Upgrade FreeRDP to version 3.28.0 or later using the system's package manager (e.g., apt-get update && apt-get upgrade freerdp2-x11 for Debian/Ubuntu, or yum update freerdp for RHEL/CentOS)
- If building from source, download FreeRDP 3.28.0 or later from the official GitHub repository (github.com/FreeRDP/FreeRDP) and rebuild
- Verify the installed version matches or exceeds 3.28.0 after upgrade
- Restart any FreeRDP server services to ensure the patched library is loaded
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-64620 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-64620 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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