6.5

CVE-2026-34835: rack

CVSS: 6.5v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-34835DEBIAN-CVE-2026-34835CGA-53wf-26hx-m78g
Published 02-04-2026Last modified 02-04-2026
Open JSON

Vulnerability summary

CVE-2026-34835 is a medium (CVSS 6.5) vulnerability in rack. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 19% of scored vulnerabilities. 1 public exploit is recorded.

Overall risk
36/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.5/10
010
Medium · v3.1 (NVD)
EPSS score
0.28%
0%100%
Low · +0.09 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits1github

Advisory lineage

Upstream 0 · Downstream 1 · Related 2
MGASA-2026-0226CGA-F9QQ-57F2-FFMPUSN-8182-1

Timeline

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

Description

Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. This issue has been patched in versions 3.1.21 and 3.2.6.

CVSS metrics

7 scores · 7 sources · 1 version

EPSS trend

Probability

0.28%

Chance of exploitation in the next 30 days

Percentile

19%

Versus all other CVEs

30-day change

+0.09 pp

From 0.19% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.28%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

1 found
  • githubUnverified

    Rack

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Chainguard29 products
  • kube-fluentd-operator< 1.18.2-r60 | < 1.18.2-r67
  • logstash-8.17All versions (No fix recorded)
  • logstash-8.17-iamguarded-compatAll versions (No fix recorded)
  • logstash-8.17-with-output-opensearchAll versions (No fix recorded)
  • logstash-8.18All versions (No fix recorded)
Wolfi4 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
Debian1 product
  • ruby-rack< 3.1.20-0+deb13u2 | < 3.2.6-2
Rack1 product
  • rack≥ 3.0.0.beta1, < 3.1.21 | ≥ 3.0.0, < 3.1.21 | ≥ 3.2.0, < 3.2.6
RubyGems1 product
  • rack≥ 3.0.0.beta1, < 3.1.21 | ≥ 3.2.0, < 3.2.6
Ubuntu1 product
  • ruby-rack< 3.1.16-0.1ubuntu0.3 | All versions (No fix recorded)

6 vendors · 37 products

References

9 links