CVE-2026-26961VulnerabilityPublished 2 Apr 2026Updated 3 Nov 2026

Ruby rack: Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser extracts the boundary parameter from

Affects ruby-rackSource GCVE Database

Compare

Not known to be exploited · CVSS 5.3 Medium · fixed in 2.1.4-5ubuntu1.2+esm3 : update ruby-rack when convenient.

Data as of 3 Nov 2026, 23:21 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 2.1.4-5ubuntu1.2+esm3, 2.2.7-1ubuntu0.7, 3.1.16-0.1ubuntu0.3

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade the Ubuntu ruby-rack to 2.1.4-5ubuntu1.2+esm3 (package) or 2.2.7-1ubuntu0.7 (package) or 3.1.16-0.1ubuntu0.3 (package).

Patches and advisories

ubuntu.com/security/notices/USN-8182-1 (opens in a new tab)

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTSruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=resolute`Other threats	Affected 3.1.16-0.1 – 3.2.4-1ubuntu1.1 5 affected builds	Fixed in–
Ubuntu 25.10ruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=questing`Other threats	Affected <3.1.16-0.1ubuntu0.3	Fixed in 3.1.16-0.1ubuntu0.3
Ubuntu 24.04 LTSruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=noble`Other threats	Affected <2.2.7-1ubuntu0.7	Fixed in 2.2.7-1ubuntu0.7
Ubuntu Pro 22.04 LTSruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=esm-apps/jammy`Other threats	Affected 2.1.4-5ubuntu1+esm2 – 2.1.4-5ubuntu1+esm5 <2.1.4-5ubuntu1.2+esm3 4 affected builds	Fixed in 2.1.4-5ubuntu1.2+esm3
Ubuntu Pro 18.04 LTSruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=esm-apps/bionic`Other threats	Affected 1.6.4-4 – 1.6.4-4ubuntu0.2+esm10 12 affected builds	Fixed in–
Ubuntu Pro 16.04 LTSruby-rack`pkg:deb/ubuntu/ruby-rack?arch=source&distro=esm-apps/xenial`Other threats	Affected 1.5.2-4 – 1.6.4-3ubuntu0.2+esm10 14 affected builds	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Ruby Rack versions 2.2.23, 3.1.21, and 3.2.6. Users should update to these or later versions to remediate the vulnerability. For Ubuntu users, security updates are provided in package versions 2.1.4-5ubuntu1.2+esm3, 2.2.7-1ubuntu0.7, and 3.1.16-0.1ubuntu0.3. After updating, restart any applications using Rack to apply the fixes.

Description

A vulnerability in Ruby Rack prior to versions 2.2.23, 3.1.21, and 3.2.6 allows improper parsing of multipart/form-data boundaries. Rack::Multipart::Parser uses a greedy regular expression that selects the last boundary parameter when multiple are present, while upstream proxies or intermediaries may use the first. This mismatch can enable an attacker to bypass upstream inspection and cause Rack to parse a different multipart body than validated. The issue has been fixed in the stated versions.

Impact

The vulnerability allows attackers to bypass network security filters or web application firewalls by exploiting the mismatch in multipart boundary parsing between Rack and upstream intermediaries. This can lead to smuggling of multipart content that bypasses inspection, potentially causing downstream parsing issues or denial of service. The CVSS score is 5.3 (medium severity) with no confidentiality or availability impact but with integrity impact.

References

Community reviews

Loading reviews…