CVE-2026-26962 | Rack: Header injection in multipart requests

Rack is a modular Ruby web server interface. From version 3.2.0 to before version 3.2.6, Rack::Multipart::Parser unfolds folded multipart part headers incorrectly. When a multipart header contains an obs-fold sequence, Rack preserves the embedded CRLF in parsed parameter values such as filename or name instead of removing the folded line break during unfolding. As a result, applications that later reuse those parsed values in HTTP response headers may be vulnerable to downstream header injection or response splitting. This issue has been patched in version 3.2.6.

Published: 2026-04-02 Last update: 2026-04-21 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-26962 is rated Low Risk (21.1/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.02%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-26962

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-21 0.05% 0.02% -0.03%
2 2026-04-08 0.04% 0.05% +0.01%
3 2026-04-03 — 0.04% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-26962

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.8 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 2.5 [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 2.5 [email protected]

Weakness enumeration for CVE-2026-26962

GitHub Security Advisory for CVE-2026-26962

GHSA-rx22-g9mx-qrhv · Severity: medium · Ecosystem: rubygems — Rack's improper unfolding of folded multipart headers preserves CRLF in parsed parameter values

OS Trackers for CVE-2026-26962

vendor priority summary link
debian not yet assigned CVE-2026-26962 not yet assigned priority: Debian including 1 source packages (ruby-rack), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-26962
redhat medium — https://access.redhat.com/security/cve/CVE-2026-26962
suse medium CVE-2026-26962 severity moderate: SUSE including 1 source package names (hawk2), 6 product×package rows across 6 product lines (SUSE Linux Enterprise High Availability Extension 12 SP5, SUSE Linux Enterprise High Availability Extension 15 SP4, … (6 product lines)): Known Not Affected 6. https://www.suse.com/security/cve/CVE-2026-26962/
ubuntu medium CVE-2026-26962 medium priority: Ubuntu including 1 source packages (ruby-rack), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): ignored 5, released 2, needed 1, not-affected 1. https://ubuntu.com/security/CVE-2026-26962

Affected software / configurations for CVE-2026-26962

Vendor Product Version Raw CPE
rack rack >= 3.2.0, < 3.2.6 cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*

References for CVE-2026-26962

cvelogic Threat Intelligence