CVE-2023-41037

Cleartext Signed Message Signature Spoofing in openpgp

Workarounds

Check the contents of verificationResult.data to see what data was actually signed, rather than visually trusting the contents of the armored message.

References

Similar CVE: https://sec-consult.com/vulnerability-lab/advisory/cleartext-message-spoofing-in-go-cryptography-libraries-cve-2019-11841/

OpenPGP Cleartext Signed Messages are cryptographically signed messages where the signed text is readable without special tools:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

This text is signed.
-----BEGIN PGP SIGNATURE-----

wnUEARMIACcFgmTkrNAJkInXCgj0fgcIFiEE1JlKzzDGQxZmmHkYidcKCPR+
BwgAAKXDAQDWGhI7tPbhB+jlKwe4+yPJ+9X8aWDUG60XFNi/w8T7ZgEAsAGd
WJrkm/H5AXGZsqyqqO6IWGF0geTCd4mWm/CsveM=
-----END PGP SIGNATURE-----

These messages typically contain a "Hash: ..." header declaring the hash algorithm used to compute the signature digest.
OpenPGP.js up to v5.9.0 ignored any data preceding the "Hash: ..." texts when verifying the signature. As a result, malicious parties could add arbitrary text to a third-party Cleartext Signed Message, to lead the victim to believe that the arbitrary text was signed.

A user or application is vulnerable to said attack vector if it verifies the CleartextMessage by only checking the returned verified property, discarding the associated data information, and instead visually trusting the contents of the original message:

const cleartextMessage = `
-----BEGIN PGP SIGNED MESSAGE-----
This text is not signed but you might think it is. Hash: SHA256

This text is signed.
-----BEGIN PGP SIGNATURE-----

wnUEARMIACcFgmTkrNAJkInXCgj0fgcIFiEE1JlKzzDGQxZmmHkYidcKCPR+
BwgAAKXDAQDWGhI7tPbhB+jlKwe4+yPJ+9X8aWDUG60XFNi/w8T7ZgEAsAGd
WJrkm/H5AXGZsqyqqO6IWGF0geTCd4mWm/CsveM=
-----END PGP SIGNATURE-----
`;
const message = await openpgp.readCleartextMessage({ cleartextMessage });
const verificationResult = await verifyCleartextMessage({ message, verificationKeys });
console.log(await verificationResult.verified); // output: true
console.log(verificationResult.data); // output: 'This text is signed.'

Since verificationResult.data would always contain the actual signed data, users and apps that check this information are not vulnerable.
Similarly, given a CleartextMessage object, retrieving the data using getText() or the text field returns only the contents that are considered when verifying the signature.
Finally, re-armoring a CleartextMessage object (using armor() will also result in a "sanitised" version, with the extraneous text being removed.
Because of this, we consider the vulnerability impact to be very limited when the CleartextMessage is processed programmatically; this is reflected in the Severity CVSS assessment, specifically in the scope's score ("Unchanged").

CVE-2023-41037 has a CVSS score of 4.3 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.10.11, 5.10.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

• v5.10.1 (current stable version) will reject messages when calling openpgp.readCleartextMessage()
• v4.10.11 (legacy version) will reject messages when calling openpgp.cleartext.readArmored()

1. What is CVE-2023-41037? CVE-2023-41037 is a medium-severity security vulnerability in openpgp (npm), affecting versions < 4.10.11. It is fixed in 4.10.11, 5.10.1.
2. How severe is CVE-2023-41037? CVE-2023-41037 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of openpgp are affected by CVE-2023-41037? openpgp (npm) versions < 4.10.11 is affected.
4. Is there a fix for CVE-2023-41037? Yes. CVE-2023-41037 is fixed in 4.10.11, 5.10.1. Upgrade to this version or later.
5. Is CVE-2023-41037 exploitable, and should I be worried? Whether CVE-2023-41037 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-41037 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-41037?
   • Upgrade openpgp to 4.10.11 or later
   • Upgrade openpgp to 5.10.1 or later

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