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Fencer Vulns
medium 4.0

CVE-2021-31406 json

Timing side channel vulnerability in endpoint request handler in Vaadin 15-19

published 2021-04-19 5 y ago modified 2026-06-17 4 mo ago also GHSA-p7jq-v8jp-j424 , EUVD-2021-0850

cvss
4.0
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 11%
public exploits
0
none known

Summary

Non-constant-time comparison of CSRF tokens in endpoint request handler in com.vaadin:flow-server versions 3.0.0 through 5.0.3 (Vaadin 15.0.0 through 18.0.6), and com.vaadin:fusion-endpoint version 6.0.0 (Vaadin 19.0.0) allows attacker to guess a security token for Fusion endpoints via timing attack.

Patch / fix

  • maven com.vaadin:flow-server 5.0.4, 6.0.1
  • vaadin flow 5.0.4
  • vaadin vaadin 18.0.7

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 11% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.0 CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD 3.1 2.5 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 2.0 1.9 AV:L/AC:M/Au:N/C:P/I:N/A:N
GitHub 3.1 4.0 CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
maven com.vaadin:flow-server
>=3.0.0, <5.0.4
>=6.0.0, <6.0.1
5.0.4
6.0.1

Affected products

  • Vaadin Vaadin
  • Vaadin flow-server

Classification

Weakness
  • CWE-208 Observable Timing Discrepancy
  • CWE-203 Observable Discrepancy

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.