Default client side session signing key is highly predictable

published 2021-06-29 5 y ago modified 2026-07-08 4 mo ago also GHSA-2cc5-23r7-vc4v , EUVD-2021-1431

cvss: 4.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 18%
public exploits: 0; none known

Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, the client side session module uses the application startup time as the signing key by default. This means that if an attacker can determine this time, and if encryption is not also used (which is recommended, but is not on by default), the session data could be tampered with by someone with the ability to write cookies. The default configuration is unsuitable for production use as an application restart renders all sessions invalid and is not multi-host compatible, but its use is not actively prevented. As of Ratpack 1.9.0, the default value is a securely randomly generated value, generated at application startup time. As a workaround, supply an alternative signing key, as per the documentation's recommendation.

Patch / fix

fixed in 2

maven io.ratpack:ratpack-session 1.9.0
ratpack_project ratpack 1.9.0

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 18% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.4	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
NVD	3.1	3.1	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
NVD	2.0	3.5	AV:N/AC:M/Au:S/C:N/I:P/A:N
GitHub	3.1	4.4	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
maven	io.ratpack:ratpack-session	<1.9.0	1.9.0

Affected products

ratpack ratpack

Classification

Weakness

CWE-340 Generation of Predictable Numbers or Identifiers
CWE-330 Use of Insufficiently Random Values

References

github.com /ratpack/ratpack/security/advisories/GHSA-2cc5-23r7-vc4v
web, third-party-advisory
github.com /ratpack/ratpack/blob/29434f7ac6fd4b36a4495429b70f4c8163100332/ratpack-session/src/main/java/ratpack/session/c
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2021-29480
advisory
github.com /ratpack/ratpack
package

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.

Summary