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CVE.org (no NVD analysis yet)· CNA GitHub_M

CVE-2026-125108: Rack: Multipart boundary ambiguity guard in Rack::Multipart::Parser can be bypassed with a quoted boundary value, allowing WAF bypass

LowCVSS 3.7 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 14/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.24% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: ruby-rack (Debian:14) 3.2.8-1; rack (RubyGems) 3.1.23, 3.2.8, 2.2.25.

Low priority for now. Upgrade to ruby-rack (Debian:14) 3.2.8-1; rack (RubyGems) 3.1.23, 3.2.8, 2.2.25 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Rack is a modular Ruby web server interface. Prior to 2.2.25, 3.1.23, and 3.2.8, Rack::Multipart::Parser.parse_boundary can skip a leading empty or quoted boundary parameter in a multipart Content-Type header and accept a later parameter. Rack can therefore parse a request body with a boundary that a conforming intermediary would not derive, allowing form fields or file uploads to reach an application without the intended proxy or web application firewall inspection. This issue is fixed in versions 2.2.25, 3.1.23, and 3.2.8.

Published
Nov 9, 2026
Updated
Nov 12, 2026
EPSS
0.2% · 15th percentile

Report tools

JSON

Action score

14

Monitor

Low priority for now.

CVSS
14 / 40 · 3.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CNA vs NVD score

NVD
—
CNA · GitHub_M
3.7
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-125108

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • rack rack

    • < 2.2.25, >= 3.0, < 3.1.23, >= 3.2, < 3.2.8affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12ruby-rackfrom 0—
Debian:14ruby-rackbefore 3.2.8-13.2.8-1
RubyGemsrackfrom 3.0.0 · before 3.1.233.1.23
RubyGemsrackfrom 3.2.0 · before 3.2.83.2.8
RubyGemsrackbefore 2.2.252.2.25

Same product

rack: all records

Other highest-scoring records for the same primary product.

  • CVE-2024-25126Rack ReDos in content type parsing (2nd degree polynomial)
    41Plan
  • CVE-2024-26146Possible Denial of Service Vulnerability in Rack Header Parsing
    31Monitor
  • CVE-2023-27530A DoS vulnerability exists in Rack <v3.0.4.2, <v2.2.6.3, <v2.1.4.3 and <v2.0.9.3 within in the Multipart MIME parsing code in which could…
    31Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-34827Apr 2, 2026 · Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
    30Monitor
  • ← EarlierCVE-2026-34835Apr 2, 2026 · Rack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass.
    26Monitor
  • Later →CVE-2026-125109Nov 9, 2026 · Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835
    19Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:ruby-rack3.2.8-1 · Debian:14Package registry (OSV)
RubyGems:rack2.2.25Package registry (OSV)
RubyGems:rack3.1.23Package registry (OSV)
RubyGems:rack3.2.8Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recorded+1 d
  3. TodayNov 13, 2026+4 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-32762221 days apartRack: Forwarded Header semicolon injection enables Host and Scheme spoofing
    26Monitor
  • CVE-2026-26961221 days apartRack: Multipart Boundary Parsing Ambiguity allowing WAF Bypass
    21Monitor

Not on record for this CVE: researcher credit · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-436 · Interpretation Conflict

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records