5.3

CVE-2026-26961: rack Interpretation Conflict

CVSS: 5.3v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-26961DEBIAN-CVE-2026-26961CGA-386q-rm7q-gh5r
Published 02-04-2026Last modified 03-04-2026
Open JSON

Vulnerability summary

CVE-2026-26961 is a medium (CVSS 5.3) Interpretation Conflict vulnerability in rack. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18.5% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (NVD)
EPSS score
0.27%
0%100%
Low · +0.02 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 5 · Related 6
MGASA-2026-0226OPENSUSE-SU-2026:10508-1OPENSUSE-SU-2026:21640-1SUSE-SU-2026:23321-1SUSE-SU-2026:2487-1CGA-9JWX-CW7V-PJXH

Timeline

  1. 02-04-2026
    PublishedVulnerability first disclosed.
  2. 03-04-2026
    Last modifiedVulnerability information updated.

Description

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser extracts the boundary parameter from multipart/form-data using a greedy regular expression. When a Content-Type header contains multiple boundary parameters, Rack selects the last one rather than the first. In deployments where an upstream proxy, WAF, or intermediary interprets the first boundary parameter, this mismatch can allow an attacker to smuggle multipart content past upstream inspection and have Rack parse a different body structure than the intermediary validated. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

CVSS metrics

7 scores · 7 sources · 1 version

EPSS trend

Probability

0.27%

Chance of exploitation in the next 30 days

Percentile

19%

Versus all other CVEs

30-day change

+0.02 pp

From 0.25% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.27%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard57 products
  • gitlab-exporter-18.10< 18.10.3-r0
  • gitlab-exporter-18.7All versions (No fix recorded)
  • gitlab-exporter-18.8< 18.8.9-r0
  • gitlab-exporter-18.9< 18.9.5-r0
  • gitlab-rails-ce-18.1< 18.1.6-r13
Wolfi8 products
  • kube-fluentd-operator< 1.18.2-r60 | < 1.18.2-r67
  • logstash-9.3< 9.3.3-r2
  • logstash-9.3-iamguarded-compat< 9.3.3-r2
  • logstash-9.3-with-output-opensearch< 9.3.3-r2
  • ruby3.2-rack-2.2< 2.2.23-r0
Debian1 product
  • ruby-rack< 2.2.22-0+deb12u2 | < 3.1.20-0+deb13u2 | < 3.2.6-2
Rack1 product
  • rack≥ 3.0.0.beta1, < 3.1.21 | < 2.2.23 | ≥ 3.0.0, < 3.1.21 | ≥ 3.2.0, < 3.2.6
RubyGems1 product
  • rack< 2.2.23 | ≥ 3.0.0.beta1, < 3.1.21 | ≥ 3.2.0, < 3.2.6
Ubuntu1 product
  • ruby-rackAll versions (No fix recorded) | < 2.1.4-5ubuntu1.2+esm3 | < 2.2.7-1ubuntu0.7 | < 3.1.16-0.1ubuntu0.3

6 vendors · 69 products

References

9 links