CVE-2026-39324: rack rack-session Improper Authentication
CVSS: 9.8v3.1CriticalAnalyzed
AliasesUBUNTU-CVE-2026-39324USN-8190-1DEBIAN-CVE-2026-39324CGA-2p83-3r2m-76g5CGA-46f6-cg5v-m8vcCGA-4q7j-jrxv-x62vCGA-77p3-475p-2cxfCGA-7j8f-mh5w-6hxfCGA-7v5h-mj6x-5hrwCGA-983g-h3cx-8q76CGA-ffpr-fhc7-5m83CGA-gm9h-gq72-ghg9CGA-m396-95h7-948vCGA-r6v8-r4vx-jrr2CGA-rc9v-jxq4-6822CGA-rvwh-3v79-5wm7CGA-vcmx-9h6r-p57ropenSUSE-SU-2026:10604-1CGA-22wg-rjcr-w7r8CGA-33vp-8mx3-w8xmCGA-34gf-g6jp-6c2vCGA-3v8q-f3g9-6vrfCGA-3wgx-cp28-3xg9CGA-3wj6-6wh2-9q6rCGA-3wqq-c6vh-9wm8CGA-543c-rc6m-q6jxCGA-57p8-7w5h-m4vjCGA-5g9q-gcjf-8hhhCGA-5wjp-h269-m5qmCGA-5xxg-g9gc-763rCGA-68hj-693g-f4jjCGA-6xjf-vh3w-fg5hCGA-7hhx-6gph-g48cCGA-7j9w-g8f2-m3qcCGA-7jq9-fmr6-jvwwCGA-8233-cjfj-59f8CGA-82qf-m8c6-j3mpCGA-879f-96h5-c827CGA-89xq-93xh-3636CGA-8h56-vrf5-rc7mCGA-8vch-wpmx-5pmfCGA-9cqj-cpm7-84x7CGA-9j7m-xm29-xc37CGA-cmgf-f4rq-qq5wCGA-cqrv-79v3-55jvCGA-f884-gc24-45c6CGA-fvxj-v4vv-9gg2CGA-gg52-wrv6-v23xCGA-h9vc-j349-4v7xCGA-hh3p-qg63-q8mjCGA-hvf8-rq74-hf2hCGA-j4q8-vp23-h4h5CGA-m2jh-96hc-c624CGA-m5j3-vfjh-fr6qCGA-mc63-5pgw-6cvjCGA-mx5h-7675-m6cfCGA-ph8c-w9w8-94qvCGA-phg3-mwgh-w9fwCGA-prhj-j487-r8w3GHSA-33qg-7wpp-89cqCGA-q2vv-qfm6-hf5vCGA-q84p-vm47-crg5CGA-qq86-49hq-233vCGA-qwgj-83h7-fq5cCGA-qwqw-gpcg-rv6cCGA-qxp4-6h35-r95fCGA-r3qm-4r9f-v27jCGA-rr3p-mrph-mvc9CGA-v2wq-jvmp-mc6cCGA-v3cr-q2v9-gg3wCGA-vggr-pq36-cq83CGA-vh66-hfmv-2jghCGA-vr6p-72gm-gx95CGA-w4qj-79q2-f9ggCGA-wx76-r4cq-75hjCGA-xphj-35qg-6568CGA-xwc8-46vv-4m9m
Published 07-04-2026Last modified 08-04-2026
Vulnerability summary
CVE-2026-39324 is a critical (CVSS 9.8) Improper Authentication vulnerability in rack rack-session. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18% of scored vulnerabilities.
CVSS score
9.8/10
010
Critical · v3.1 (NVD)EPSS score
0.27%
0%100%
Low · 0.00 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 0 · Related 2Timeline
- 07-04-2026PublishedVulnerability first disclosed.
- 08-04-2026Last modifiedVulnerability information updated.
Description
Rack::Session is a session management implementation for Rack. From 2.0.0 to before 2.1.2, Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie. This allows an unauthenticated attacker to supply a crafted session cookie that is accepted as valid session data without knowledge of any configured secret. Because this mechanism is used to load session state, an attacker can manipulate session contents and potentially gain unauthorized access. This vulnerability is fixed in 2.1.2.
CVSS metrics
9 scores · 7 sources · 2 versionsCritical 9.3Preferred score · CVE.org (CNA)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:NSources6 sources · 9.1–9.3
- OSV · UbuntuEcosystem advisory · calculated9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · WolfiEcosystem advisory · calculated9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · RubygemsEcosystem advisory · calculated9.1CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:NDiffers
- NVDNIST9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Critical 9.8Preferred score · NVD (NIST)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSourcesAll 3 agree
- OSV · UbuntuEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.27%
Chance of exploitation in the next 30 days
Percentile
18%
Versus all other CVEs
30-day change
0.00 pp
From 0.27% on 20-09-2026
20-09-202620-10-2026
EPSS score0.27%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-287Improper AuthenticationWhen an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
- CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
- CWE-502Deserialization of Untrusted DataThe product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
- CWE-565Reliance on Cookies without Validation and Integrity CheckingThe product relies on the existence or values of cookies when performing security-critical operations, but it does not properly ensure that the setting is valid for the associated user.
Affected systems
Chainguard36 products
- 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)
- logstash-8.18-iamguarded-compatAll versions (No fix recorded)
Wolfi7 products
- 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-rails-8.1< 8.1.3-r2 | < 8.1.3-r3
- ruby3.3-rails-8.1< 8.1.3-r4 | < 8.1.3-r3
Debian1 product
- ruby-rack-session< 2.1.1-0.1+deb13u1 | < 2.1.1-0.2
Opensuse1 product
- rubygem-rack-session&distro=openSUSE Tumbleweed< 2.1.2-1.1
Rack1 product
- rack-session≥ 2.0.0, < 2.1.2
RubyGems1 product
- rack-session≥ 2.0.0, < 2.1.2
Ubuntu1 product
- ruby-rack-session< 2.1.1-0.1ubuntu0.26.04.1 | < 2.1.1-0.1ubuntu0.1
7 vendors · 48 products
References
11 links- github.com/rack/rack-session/security/advisories/GHSA-33qg-7wpp-89cqX Refsource CONFIRMREPORTAdvisoryWEBMitigationVendor Advisory
- github.com/rack/rack-sessionPACKAGE