Raw vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:N/VA:H/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XSummary
CVE-2026-22858 is a medium-severity Out-of-bounds Read (CWE-125) vulnerability in Freerdp Freerdp. Its CVSS base score is 5.6 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 46th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-22858 is a global buffer overflow vulnerability (CWE-125: Out-of-bounds Read; CWE-758: Reliance on Undefined, Unspecified, or Implementation-Defined Behavior) in the Base64 decoding path of FreeRDP, an open-source implementation of the Remote Desktop Protocol. The flaw affects FreeRDP versions prior to 3.20.1 and stems from implementation-defined char signedness on Arm/AArch64 builds, where plain char is treated as unsigned. This causes the guard condition c <= 0 to optimize into c != 0, allowing non-ASCII bytes (e.g., 0x80-0xFF) to bypass intended range restrictions and serve as indices into a global lookup table, resulting in out-of-bounds access.
The vulnerability carries a CVSS v3.1 base score of 9.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H), indicating it is exploitable over the network with low attack complexity, no privileges or user interaction required, and unchanged impact scope. Unauthenticated remote attackers can trigger the issue by supplying malicious input during Base64 decoding in RDP sessions, potentially achieving high confidentiality impact through information disclosure or high availability impact via crashes and denial of service.
FreeRDP addresses this vulnerability in version 3.20.1. Security practitioners should upgrade affected systems to 3.20.1 or later. Additional details are available in the project's security advisory (GHSA-qmqf-m84q-x896) and release notes at https://github.com/FreeRDP/FreeRDP/releases/tag/3.20.1.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2669
Vulnerability Data
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.20.1, global-buffer-overflow was observed in FreeRDP's Base64 decoding path. The root cause appears to be implementation-defined char signedness: on Arm/AArch64 builds, plain char is treated as unsigned, so…
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the guard c <= 0 can be optimized into a simple c != 0 check. As a result, non-ASCII bytes (e.g., 0x80-0xFF) may bypass the intended range restriction and be used as an index into a global lookup table, causing out-of-bounds access. This vulnerability is fixed in 3.20.1.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation directly finds out-of-bounds read flaws through static analysis, fuzzing, and dynamic bounds checks.
Mandating a documented development process and coding standards directly discourages dependence on unspecified behavior.
Secure engineering principles require bounds checking and memory-safe constructs that stop out-of-bounds reads from being introduced.
Process isolation confines the effects of an out-of-bounds read to the compromised process.
Input validation rejects malformed indices or lengths that would otherwise cause reads outside buffer bounds.
Memory-protection mechanisms limit the exploitability and blast radius of a successful out-of-bounds write.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure-development practices such as bounds checking and memory-safe languages directly prevent out-of-bounds reads.
Vulnerability scanning and recording can discover instances of out-of-bounds reads after code is deployed.
Consistent hardened configurations reduce the chance of relying on unspecified implementation details.
Routine patching replaces vulnerable code containing out-of-bounds read flaws.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance includes fuzzing and static analysis that detect out-of-bounds read defects before release.
Logging can record evidence of an out-of-bounds read but does not prevent the weakness itself.
Secure development life cycle mandates input validation and bounds checking that directly prevent out-of-bounds reads.
Application security requirements include explicit bounds and memory-safety specifications that mitigate buffer over-reads.
Secure system architecture and engineering principles require memory-safe design patterns and runtime protections against out-of-bounds access.
Secure coding standards explicitly forbid unsafe pointer arithmetic and mandate bounds-checked reads, eliminating CWE-125.