CVE-2026-21862
Published: 03 February 2026
Summary
CVE-2026-21862 is a high-severity Authentication Bypass by Spoofing (CWE-290) vulnerability in Rustfs Rustfs. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 13.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Reveals spoofed logon attempts through unexpected previous logon timestamps upon legitimate login.
Training specifically addresses recognizing spoofed communications and phishing that enable authentication bypass.
Requiring verifiable identity evidence at appropriate assurance levels makes it substantially harder for attackers to successfully spoof or impersonate users to obtain accounts.
Unique device authentication makes successful spoofing of device identity substantially more difficult to achieve.
Unique identification of non-organizational users reduces the feasibility of authentication bypass by spoofing.
Unique identification and authentication of services before communications makes spoofing of service identities substantially harder.
Isolated trusted path ensures the user interacts only with genuine system components, preventing spoofing of authentication interfaces or prompts.
Directly counters DNS response spoofing by requiring cryptographic origin authentication artifacts from the authoritative source.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability directly enables remote exploitation of a public-facing object storage service to bypass IP-based access controls via header spoofing.
NVD Description
RustFS is a distributed object storage system built in Rust. Prior to version alpha.78, IP-based access control can be bypassed: get_condition_values trusts client-supplied X-Forwarded-For/X-Real-Ip without verifying a trusted proxy, so any reachable client can spoof aws:SourceIp and satisfy IP-allowlist policies.…
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This issue has been patched in version alpha.78.
Deeper analysisAI
CVE-2026-21862 affects RustFS, a distributed object storage system built in Rust. Prior to version alpha.78, the vulnerability enables bypass of IP-based access control in the get_condition_values function, which trusts client-supplied X-Forwarded-For or X-Real-Ip headers without verifying a trusted proxy. This allows attackers to spoof the aws:SourceIp condition and satisfy IP-allowlist policies. The issue is rated 7.5 on the CVSS 3.1 scale (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) and is associated with CWE-290.
Any network-reachable client can exploit this vulnerability without authentication or user interaction. By supplying forged X-Forwarded-For or X-Real-Ip headers, attackers can impersonate an allowed IP address, bypassing IP restrictions on object storage access. This results in high integrity impact, potentially enabling unauthorized data modification or policy evasion, though it does not compromise confidentiality or availability.
The GitHub Security Advisory at https://github.com/rustfs/rustfs/security/advisories/GHSA-fc6g-2gcp-2qrq details the patch in RustFS version alpha.78, which addresses the trust issue in header processing. Security practitioners should upgrade to alpha.78 or later to mitigate the vulnerability.
Details
- CWE(s)