CVE-2021-31403

Token disclosure via non-constant-time comparison

Published Apr 23, 2021 · Updated Sep 16, 2024

Timing discrepancy in Vaadin 7.0.0 through 7.7.23 and 8.0.0 through 8.12.2 allows attackers to infer tokens from UIDL requests. The UIDL handler compares supplied CSRF tokens without constant-time semantics, so invalid-request rejection latency varies with token content. Exploitation requires repeated timing measurements; a recovered token permits blind data submission as the user or listening to WebSocket-published data.

CVSS severity4.0
Medium
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing discrepancy in Vaadin 7.0.0 through 7.7.23 and 8.0.0 through 8.12.2 allows attackers to infer tokens from UIDL requests. The UIDL handler compares supplied CSRF tokens without constant-time semantics, so invalid-request rejection latency varies with token content. Exploitation requires repeated timing measurements; a recovered token permits blind data submission as the user or listening to WebSocket-published data.

The record

CVE
CVE-2021-31403
Published
Apr 23, 2021
Updated
Sep 16, 2024
Vendor
Vaadin
Product
Vaadin Framework
Classifications
CWE-203, CWE-208
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.0.0 <* changes=[{"at":"8.0.0","status":"affected"}]

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Vaadin · Vaadin Frameworkversion=7.0.0 <* changes=[{"at":"8.0.0","status":"affected"}]
Vaadin · Vaadin Serverversion=7.0.0 <* changes=[{"at":"8.0.0","status":"affected"}]

Published CVSS scores

1.9NIST NVDAV:L/AC:M/Au:N/C:P/I:N/A:N
4.0Vaadin Ltd.CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
2.5NIST NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-203Observable Discrepancy
CWE-208Observable Timing Discrepancy

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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