How severe is CVE-2026-21862?

No CVSS score has been assigned to CVE-2026-21862 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-21862?

CVE-2026-21862 affects the following packages: rustfs (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2026-21862?

Update rustfs to 1.0.0-alpha.78 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21862 is resolved across your whole dependency graph.

How do I detect CVE-2026-21862 in my crates.io dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rustfs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-21862 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-21862?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-21862 can be triaged on real exposure rather than presence alone.

Is CVE-2026-21862 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-21862 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-21862?

CVE-2026-21862 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 12th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-21862?

CVE-2026-21862 is classified as CWE-290 (CWE-290). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-21862 published, and has it been updated?

CVE-2026-21862 was published on February 3, 2026 and was last updated on February 3, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀 crates.io

Not in CISA KEV

CVE-2026-21862 — rustfs

Fix: rustfs/rustfs@b4ba62f

CVE-2026-21862 is a CWE-290 vulnerability in rustfs. A fix is available for rustfs — see the affected versions and patch details below.

RustFS has SourceIp bypass via spoofed X-Forwarded-For/Real-IP headers

Published

Feb 3, 2026

Updated

Feb 3, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 25, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-21862.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs12th percentile — riskier than 12% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected

🦀rustfs

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

Summary

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.

Details

Vulnerable code: rustfs/src/auth.rs:289-304 sets remote_addr from X-Forwarded-For/X-Real-Ip, then inserts SourceIp via get_source_ip_raw, with no trust boundary or proxy validation:
- let remote_addr = header.get("x-forwarded-for").and_then(...).or_else(|| header.get("x-real-ip")...).unwrap_or("127.0.0.1");
- args.insert("SourceIp", vec![get_source_ip_raw(header, remote_addr)]);
This value feeds IAM/bucket policy evaluation in rustfs/src/storage/access.rs (authorization path), so any request that forges the header can meet aws:SourceIp conditions.
No authentication is required beyond the request itself; the header is taken at face value even on direct connections.

PoC

rustfs-auth-trusted-ip-header-spoofing-poc.tar.gz

Steps (already included in rustfs-auth-trusted-ip-header-spoofing-poc/):

Start RustFS with two local volumes, e.g.:

     mkdir -p /tmp/rustfs-data1 /tmp/rustfs-data2
     RUSTFS_ACCESS_KEY=devadmin RUSTFS_SECRET_KEY=devadmin \
       cargo run --bin rustfs -- --address 0.0.0.0:9000 \
       /tmp/rustfs-data1 /tmp/rustfs-data2

From rustfs-auth-trusted-ip-header-spoofing-poc/, run:

     ENDPOINT=http://127.0.0.1:9000 make run

 The script:
  - Creates bucket `rustfs-trusted-ip-poc`.
  - Applies a bucket policy allowing `s3:ListBucket` only from `10.0.0.5/32` (`Principal: {"AWS":["*"]},` Resource array).
  - Sends three unauthenticated `ListBucket` calls:
      - Baseline (no spoof) → HTTP 403.
      - Spoofed `X-Forwarded-For: 10.0.0.5` → HTTP 200 (policy bypass).
      - Spoofed `X-Forwarded-For: 1.2.3.4` → HTTP 403.
  - Responses saved to `poc-baseline.xml`, `poc-spoofed.xml`, `poc-deny.xml`.

Impact

Vulnerability type: Authorization bypass of IP-allowlist (aws:SourceIp) via header spoofing.
Who is impacted: Any deployment relying on aws:SourceIp in IAM/bucket policies for S3 operations. Attackers with network reach to RustFS can forge forwarded-IP headers to gain list/read/write where IP restrictions were meant to block them.

Credits

Identified by SecMate (https://secmate.dev) automated analysis and validated during manual triage.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`rustfs`	all versions	1.0.0-alpha.78`cargo update -p rustfs --precise 1.0.0-alpha.78`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rustfs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rustfs to 1.0.0-alpha.78 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21862 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-21862 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-21862. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### Summary 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. ### Details - Vulnerable code: `rustfs/src/auth.rs:289-304` sets `remote_addr` from `X-Forwarded-For`/`X-Real-Ip`, then inserts `SourceIp` via `get_source_ip_raw`, with no trust boundary or proxy validation: - `let remote_addr = header.get("x-forwarded-for").and_then(...).or_else(|| header.get("x-real-ip")...).unwrap_or("127.0.0.1");` - `

O3 Security · Impact-Aware SCA

Is CVE-2026-21862 in your dependencies?

O3 Security finds CVE-2026-21862 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

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