Cyber Resilience

CVE-2026-34786

Rack ≤ 2.2.23

Published
02 April 2026
Modified
24 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS Score 0.0019 9th percentile
Risk Priority 42 floored blend · peak EPSS

Summary

CVE-2026-34786 is a medium-severity Incorrect Behavior Order: Validate Before Canonicalize (CWE-180) vulnerability in Rack Rack. Its CVSS base score is 5.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result,…

more

a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

CWE(s)
CWE-180

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1027 Obfuscated Files or Information Stealth
Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-34763Same product: Rack Rack
CVE-2026-34835Same product: Rack Rack
CVE-2026-34830Same product: Rack Rack
CVE-2026-32762Same product: Rack Rack
CVE-2026-22860Same product: Rack Rack
CVE-2025-27610Same product: Rack Rack
CVE-2026-26962Same product: Rack Rack
CVE-2026-26961Same product: Rack Rack
CVE-2025-27111Same product: Rack Rack
CVE-2025-25184Same product: Rack Rack

Affected Assets

rack
rack
≤ 2.2.23 · 3.0.0 — 3.1.21 · 3.2.0 — 3.2.6

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.3.8
  • V1.1.1
  • V12.1.3

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

SA-11 requires developer testing and evaluation that can discover validation-order defects after they have been coded.

SI-10 Information Input Validation good match

SI-10 requires validity checks on inputs; when implemented with canonicalization preceding validation it structurally prevents the exact ordering flaw.

SA-8 Security and Privacy Engineering Principles partial match

SA-8 mandates security engineering principles that include correct canonicalization-before-validation ordering for input handling.

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.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require correct validation order after canonicalization to prevent bypasses.

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.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect validation-order defects before deployment.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates input validation and canonicalization order, directly addressing CWE-180.

A.8.26 Application security requirements partial match
prevents

Application security requirements include proper input handling to prevent validation-before-canonicalization flaws.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles reduce the likelihood of ordering errors in input processing.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly require canonicalize-then-validate to eliminate CWE-180.

References