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Fencer Vulns
medium 5.9

CVE-2026-34830 json

Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file reads through nginx

published 2026-04-02 7 mo ago modified 2026-09-10 1 mo ago also GHSA-qv7j-4883-hwh7 , EUVD-2026-18390

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Patch / fix

  • rubygems rack 2.2.23, 3.1.21, 3.2.6
  • rack rack 2.2.23, 3.1.21, 3.2.6
  • ruby-rack Debian 12 2.2.22-0+deb12u2
  • ruby-rack Debian 13 3.1.20-0+deb13u2
  • ruby-rack Debian 14 3.2.6-2

debian advisories DEBIAN-CVE-2026-34830

  • ruby-rack Ubuntu 24.04 LTS 2.2.7-1ubuntu0.7
  • ruby-rack Ubuntu 25.10 3.1.16-0.1ubuntu0.3
  • ruby-rack Ubuntu 26.04 LTS 3.2.4-1ubuntu1.1
  • ruby-rack Ubuntu Pro 16.04 LTS 1.6.4-3ubuntu0.2+esm10
  • ruby-rack Ubuntu Pro 18.04 LTS 1.6.4-4ubuntu0.2+esm10
  • ruby-rack Ubuntu Pro 22.04 LTS 2.1.4-5ubuntu1.2+esm3

ubuntu advisories UBUNTU-CVE-2026-34830

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • rmt-server SLES for SAP applications 16.0, SLES 16.0 3.1.0-160000.1.1
  • rmt-server SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES 15 SP6-LTSS +5 more 2.27-150500.3.47.1

suse advisories SUSE-SU-2026:23321-1SUSE-SU-2026:2487-1

  • rmt-server openSUSE Leap 16.0 3.1.0-160000.1.1
  • rubygem-rack-2.2 openSUSE Tumbleweed 2.2.23-1.1

opensuse advisories openSUSE-SU-2026:21640-1openSUSE-SU-2026:10508-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34830 updated cvss 5.9

rack: Rack: Information disclosure via regular expression injection in X-Accel-Mapping header

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/vector-rhel9, openshift-logging/fluentd-rhel9, openshift-logging/eventrouter-rhel9, openshift-logging/logging-view-plugin-rhel9, openshift-logging/cluster-logging-rhel9-operator, openshift-logging/log-file-metric-exporter-rhel9, +1 more Red Hat 3scale API Management Platform 2 3scale-amp21/zync, 3scale-amp22/zync, 3scale-amp24/zync, 3scale-amp25/zync, 3scale-amp26/zync, 3scale-amp20/system, +19 more Red Hat Enterprise Linux 7 pcs, pcs-snmp, python-clufter Red Hat Enterprise Linux 8 pcs, pcs-snmp Red Hat Enterprise Linux 9 pcs, pcs-snmp, ubi9/ruby-30, ubi9/ruby-33, rhel9/ruby-30, rhel9/ruby-33 Red Hat Enterprise Linux 10 pcs
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
rubygems rack
<2.2.23
>=3.0.0.beta1, <3.1.21
>=3.2.0, <3.2.6
2.2.23
3.1.21
3.2.6

Affected products

  • rack rack

Classification

Weakness
  • CWE-625 Permissive Regular Expression

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.