CVE-2023-40021Public exploitNetwork attack vector

Unauthorized actions via CSRF token timing leak

Published Aug 16, 2023 · Updated Oct 3, 2024

Timing-based CSRF token exposure in Oppia before 3.3.2-hotfix-2 allows remote attackers to perform a logged-in user's authorized actions. CsrfTokenManager.is_csrf_token_valid uses ordinary string equality, leaking token-prefix information through response timing instead of comparing in constant time. Exploitation requires a logged-in user to visit an attacker-controlled site and completion within one second; account credentials remain unaffected.

CVSS severity5.3
Medium
EPSS probability0.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing-based CSRF token exposure in Oppia before 3.3.2-hotfix-2 allows remote attackers to perform a logged-in user's authorized actions. CsrfTokenManager.is_csrf_token_valid uses ordinary string equality, leaking token-prefix information through response timing instead of comparing in constant time. Exploitation requires a logged-in user to visit an attacker-controlled site and completion within one second; account credentials remain unaffected.

The record

CVE
CVE-2023-40021
Published
Aug 16, 2023
Updated
Oct 3, 2024
Vendor
Oppia Foundation
Product
Oppia
Classifications
CWE-203, CWE-208, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 16, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=1.1.0 <3.3.2
  2. Affected versionversion=>= 1.1.0, < 3.3.2-hotfix-2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Oppia Foundation · Oppiaversion=1.1.0 <3.3.2; version=>= 1.1.0, < 3.3.2-hotfix-2

Published CVSS scores

5.3GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-203Observable Discrepancy
CWE-208Observable Timing Discrepancy
T1189Drive-by Compromise

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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