Is there a public PoC exploit available for CVE-2026-6986?

Yes, a public proof-of-concept exploit is available for CVE-2026-6986. Prioritise patching immediately. EPSS: 0.0%.

Is there a patch available for CVE-2026-6986?

Yes, a patch is available for CVE-2026-6986. Update the affected software to the latest version immediately.

Cesanta Mongoose CVE-2026-6986

Q: What is the CVSS score of CVE-2026-6986?

CVE-2026-6986 has a CVSS 4.0 base score of 2.9 (Low). CVSS vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.0%.

EUVD-2026-25662 LOW

Improper Verification of Cryptographic Signature (CWE-347)

2026-04-25 VulDB

Jwt Attack Information Disclosure

2.9

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

2.9 LOW

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

PoC Detected

Apr 29, 2026 - 19:00 vuln.today

Public exploit code

Severity Changed

Apr 29, 2026 - 01:12 NVD

MEDIUM LOW

CVSS changed

Apr 29, 2026 - 01:12 NVD

6.3 (MEDIUM) 2.9 (LOW)

Severity Changed

Apr 25, 2026 - 17:22 NVD

LOW MEDIUM

CVSS changed

Apr 25, 2026 - 17:22 NVD

3.7 (LOW) 6.3 (MEDIUM)

Analysis Generated

Apr 25, 2026 - 17:15 vuln.today

EUVD ID Assigned

Apr 25, 2026 - 17:00 euvd

EUVD-2026-25662

Analysis Generated

Apr 25, 2026 - 17:00 vuln.today

Patch released

Apr 25, 2026 - 17:00 nvd

Patch available

CVE Published

Apr 25, 2026 - 16:30 nvd

LOW 2.9

DescriptionCVE.org

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This issue affects the function mg_aes_gcm_decrypt of the file /src/tls_aes128.c of the component GCM Authentication Tag Handler. Such manipulation leads to improper verification of cryptographic signature. The attack may be performed from remote. A high complexity level is associated with this attack. The exploitability is assessed as difficult. The exploit has been disclosed publicly and may be used. Upgrading to version 7.21 is capable of addressing this issue. It is advisable to upgrade the affected component. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

AnalysisAI

Improper verification of cryptographic signatures in Cesanta Mongoose versions up to 7.20 allows remote attackers to bypass GCM authentication tag validation in the mg_aes_gcm_decrypt function. The vulnerability has high attack complexity and requires no user interaction, but provides only integrity impact (not confidentiality or availability). Publicly available exploit code exists, and vendor has released patched version 7.21.

Technical ContextAI

The vulnerability resides in the GCM (Galois/Counter Mode) Authentication Tag Handler within the AES-128 cryptographic implementation (file src/tls_aes128.c). GCM mode provides both confidentiality and authenticity guarantees through authenticated encryption. The root cause (CWE-347: Improper Verification of Cryptographic Signature) indicates that the mg_aes_gcm_decrypt function fails to properly validate the authentication tag, which is the 16-byte cryptographic proof that ciphertext has not been tampered with. This allows an attacker to submit forged or modified ciphertext that decrypts successfully without detection of tampering, breaking the authenticity guarantee that GCM is supposed to provide. The high attack complexity reflects that crafting valid forged messages requires cryptographic sophistication or reverse-engineering the implementation.

RemediationAI

Immediately upgrade Cesanta Mongoose to version 7.21 or later, which includes the fix for improper GCM authentication tag verification. The patch is officially released by the vendor at https://github.com/cesanta/mongoose/releases/tag/7.21. If immediate upgrade is not possible, disable GCM-based encryption in Mongoose configuration and use only authenticated encryption modes where the authentication tag validation is independently verified. However, this workaround reduces cryptographic robustness and is not recommended as a long-term solution. Review any messages encrypted with Mongoose 7.20 or earlier using GCM mode for potential tampering, especially authentication tokens (JWT) and critical integrity-sensitive payloads, as attackers may have forged authenticated ciphertexts.