Forge: AES-GCM authentication bypass via unvalidated tagLength option

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, node-forge did not validate the AES-GCM tagLength option passed to start() during decryption through forge.cipher.createDecipher(). When an application derived tagLength from received data or used an unset or zero-like configuration value, a value that converted to zero together with an empty or missing authentication tag caused the calculated and supplied tags to compare as empty, so decipher.finish() accepted unauthenticated ciphertext. Applications that omit tagLength to use the 128-bit default or pass a fixed valid tag length are unaffected. This issue is fixed in version 1.4.1.

Source published

29 Oct 2026 19:17:26 UTC

Source modified

29 Oct 2026 20:24:15 UTC

Observed here

29 Oct 2026 21:48:56 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, node-forge did not validate the AES-GCM tagLength option passed to start() during decryption through forge.cipher.createDecipher(). When an application derived tagLength from received data or used an unset or zero-like configuration value, a value that converted to zero together with an empty or missing authentication tag caused the calculated and supplied tags to compare as empty, so decipher.finish() accepted unauthenticated ciphertext. Applications that omit tagLength to use the 128-bit default or pass a fixed valid tag length are unaffected. This issue is fixed in version 1.4.1.

Source published

Oct 29, 2026, 7:17:26 PM (timezone not stated)

Source modified

Oct 29, 2026, 8:24:15 PM (timezone not stated)

Observed here

6 Nov 2026 01:44:39 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, node-forge did not validate the AES-GCM tagLength option passed to start() during decryption through forge.cipher.createDecipher(). When an application derived tagLength from received data or used an unset or zero-like configuration value, a value that converted to zero together with an empty or missing authentication tag caused the calculated and supplied tags to compare as empty, so decipher.finish() accepted unauthenticated ciphertext. Applications that omit tagLength to use the 128-bit default or pass a fixed valid tag length are unaffected. This issue is fixed in version 1.4.1.

Source published

29 Oct 2026 20:17:29 UTC

Source modified

30 Oct 2026 17:18:03 UTC

Observed here

30 Oct 2026 23:47:40 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

### Summary The AES-GCM mode in forge.cipher does not validate the tagLength option passed to start(). With a tagLength of 0 or a value that converts to 0 (such as null, false, '' or '0'), the authentication tag is empty, and decipher.finish() returns true for any ciphertext and additional data when the supplied tag is empty or missing. Fixed in node-forge 1.4.1. ### Details `modes.gcm.prototype.start()` in `lib/cipherModes.js` stored the `tagLength` option without validation, and `lib/cipher.js` documented it as accepting "0-128". After processing the data, `afterFinish()` truncates the 16-byte tag with `truncate(16 % (tagLength / 8))`. For a `tagLength` that converts to 0, this is `16 % 0 = NaN`, and truncating by `NaN` empties the tag. On decryption, the start-time check that the supplied `tag` has `tagLength / 8` bytes passes for an empty tag, and the final tag comparison compares two empty strings, so `decipher.finish()` returns `true` for any ciphertext and additional data. NIST SP 800-38D section 5.2.1.2 allows only tag lengths of 128, 120, 112, 104 and 96 bits, plus 64 and 32 bits for certain applications. The fix validates `tagLength` in `start()`, for both encryption and decryption. A missing, `null` or `undefined` `tagLength` uses the default of 128 bits. Any other value is converted with `Number()` and must be one of 128, 120, 112, 104, 96, 64 or 32; otherwise `start()` throws "Invalid tag length.". Numeric strings such as `'128'` are still accepted. With a validated `tagLength`, an empty tag no longer matches the expected tag length and is rejected. ### Patches Fixed in node-forge 1.4.1. `cipher.start()` now throws an error unless `tagLength` is one of the tag lengths allowed by NIST SP 800-38D (128, 120, 112, 104, 96, 64 or 32 bits); a `null` or `undefined` `tagLength` means the default of 128 bits. ### Workarounds Do not derive `tagLength` from received data. Pass a fixed `tagLength` (or omit it to use the default of 128 bits), and check that the received tag has the expected length before calling `start()`, for example `if(tag.length !== 16) { throw new Error('Invalid tag.'); }` before `decipher.start({iv: iv, tag: tag});`. ### Proof of concept Start an AES-GCM decipher with `tagLength: 0` and an empty tag, as an application does when it derives the tag length from a received empty tag, and feed it arbitrary bytes that were never encrypted under the key: ```js var decipher = forge.cipher.createDecipher('AES-GCM', key); decipher.start({iv: iv, tag: '', tagLength: 0}); decipher.update(forge.util.createBuffer('any attacker-chosen bytes')); decipher.finish(); // <= 1.4.0: true // 1.4.1: start() throws "Invalid tag length." ``` `tagLength` values `null`, `false` and `'0'` (with an empty tag), and `tagLength: 0` with no `tag` option, give the same result on <= 1.4.0. The fix adds regression tests in `tests/unit/aes.js`. ### Impact Applications that decrypt AES-GCM data with `forge.cipher.createDecipher()` (`'AES-GCM'`) and pass a zero-like `tagLength` are affected. Typical cases are a tag length derived from the received tag, or an unset configuration value: ```js var decipher = forge.cipher.createDecipher('AES-GCM', key); decipher.start({iv: iv, tag: receivedTag, tagLength: receivedTag.length * 8}); decipher.update(forge.util.createBuffer(receivedCiphertext)); if(decipher.finish()) { /* attacker-supplied data accepted */ } ``` An attacker who can send a ciphertext with an empty tag to such an application can make it accept attacker-chosen ciphertext as authentic. Because GCM encryption is a stream cipher, an attacker who knows (part of) a captured message's plaintext can also change that plaintext to chosen values. The default (no `tagLength` option, 128 bits) and any fixed valid `tagLength` are not affected.

Source published

30 Oct 2026 23:02:09 UTC

Source modified

30 Oct 2026 23:15:05 UTC

Observed here

30 Oct 2026 23:45:44 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Publisher rating · MODERATE