CVE-2026-6458

AES-256-GCM Authentication Tag Does Not Cover First Ciphertext Blocks When AAD Is Empty

State: Published
Severity: 5.1 Medium
Published: Jun 23, 2026
Updated: Jun 24, 2026
Reserved: Apr 16, 2026

Description

Missing cryptographic step in Caliptra Core Firmware (aes_256_gcm_update module) results in an incorrect GCM authentication tag. When the streaming AES-256-GCM API is used with empty AAD, the hardware GHASH accumulator state is not saved after the first update call, causing the final tag to exclude the first batch of processed ciphertext. Ciphertext produced by that call may be modified without the tag reflecting the change.

This issue affects Core Runtime Firmware: from 2.0.0 through 2.0.1, 2.1.0.

Scores

CVSS	Score	Vector	Source
4.0	5.1 Medium	CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N	Caliptra

Weaknesses

CWE-325 Missing Cryptographic Step

Affected Products

Product	Versions
Core Runtime FirmwareCaliptra	2.0.0 through 2.0.1Affected 2.1.0Affected 2.0.2Not affected 2.1.1Not affected

References

https://github.com/chipsalliance/caliptra-sw/security/advisories/GHSA-834g-h5x6-2hqr

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