Forge: AES-GCM authentication bypass via unvalidated tagLength option (CVE-2026-119186)
Published Last modified Sources: OSV, Hersteller, CVE.org
What is affected, what to do
Update Digitalbazaar Forge to version 1.4.1.
- Affected
- Digitalbazaar Forge
lt *..1.4.1
- Digitalbazaar Forge
- Fixed in
- Digitalbazaar Forge
1.4.1
- Digitalbazaar Forge
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
5.9
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
5.9
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: OSV, Hersteller, CVE.org
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 10.7
Show all metrics
- Severity
- Medium
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 60.42 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 5.9 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 5.9
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.2 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 10.7
- Elevated — this CVE ranks above at least 10% of all CVEs scored today.
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
- CISA assessment (SSVC)
- Exploitation: proof of concept · not automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 29 October 2026
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-1284, CWE-354
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
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:
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:
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: OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| digitalbazaar | forge |
|
|
| npm | node-forge |
|
|
Vendors and products
Weakness classes (CWE)
CWE-1284Improper Validation of Specified Quantity in Input
Base
The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.
Entry at MITRE CWE-1284CWE-354Improper Validation of Integrity Check Value
Base
The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.
Entry at MITRE CWE-354
References & sources
- github.comdigitalbazaar/forge/commit/236845d96c71207259f91638d0138bba8e2f…x_refsource_MISC, web
- github.comdigitalbazaar/forge/releases/tag/v1.4.1x_refsource_MISC, web
- github.comdigitalbazaar/forge/security/advisories/GHSA-5cwg-6vw7-rj6px_refsource_CONFIRM, web
- NVD (NIST)vuln/detail/CVE-2026-119186advisory
- github.comdigitalbazaar/forgepackage
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: proof of concept, automatable: no
Show 2 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://github.com/digitalbazaar/forge/security/advisories/GHSA-5cwg-6vw7-rj6pSSVC assessment added —{"id":"CVE-2026-119186","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-29T20:23:41.622079Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
ReceivedGitHub
CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness type: CWE-354, CWE-1284
Description added or changed
Show 8 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —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.CVSS added —AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:NWeakness type (CWE) added —CWE-354Weakness type (CWE) added —CWE-1284Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/119xxx/CVE-2026-119186.json">CVE-2026-119186</a>Reference added —https://github.com/digitalbazaar/forge/commit/236845d96c71207259f91638d0138bba8e2fd624Reference added —https://github.com/digitalbazaar/forge/releases/tag/v1.4.1Reference added —https://github.com/digitalbazaar/forge/security/advisories/GHSA-5cwg-6vw7-rj6pSource identifier: security-advisories@github.com
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-119186"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-119186.svg?lang=en" alt="CVE-2026-119186 – NEOSEC Intel" height="20"></a>