TI-2021-17568 Aliases CVE-2021-40528 GHSA-8m2v-68m9-q2c7

The ElGamal implementation in Libgcrypt before 1.9.4 allows plaintext recovery because…

LOW 29CWE-327Published 2021-09-06 · Updated 2025-06-09

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: High
Impact type: Information disclosure
Confidentiality · integrity · availability: High · None · None
Fix status: Partial Red Hat: 1 fixed, 2 without a fix

Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat. Impact type from CWE-327.

Summary

The ElGamal implementation in Libgcrypt before 1.9.4 allows plaintext recovery because, during interaction between two cryptographic libraries, a certain dangerous combination of the prime defined by the receiver's public key, the generator defined by the receiver's public key, and the sender's ephemeral exponents can lead to a cross-configuration attack against OpenPGP.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.01423 73rd percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Partial Red Hat: 1 advisoryRed Hat: 1 fixed, 2 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
—	—	all versions	—	No fix listed	CNA

— Vendor— Affected all versions Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:gnupg:libgcrypt::::::::	before 1.9.4	Vulnerable	GnuPG

cpe:2.3:a:gnupg:libgcrypt:*:*:*:*:*:*:*:* Versions before 1.9.4 Vulnerable ·GnuPG

Remediation

Red Hat 1 advisory

RHSA-2022:5311 Released 2022-06-30 · Red Hat rating Moderate
libgcrypt security update
- Red Hat Enterprise Linux BaseOS (v. 8) libgcrypt-1.8.5-7.el8_6, libgcrypt-devel-1.8.5-7.el8_6

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 6	Affected	No fix planned: Out of support scope
Red Hat Enterprise Linux 7	Affected	No fix planned: Out of support scope
Red Hat Enterprise Linux BaseOS (v. 8)	Fixed	RHSA-2022:5311

Not affected: 1 product

Red Hat Enterprise Linux 9

Timeline

2026-10-02 Threatist record created from CVE-2021-40528
2026-10-03 Alias added: GHSA-8m2v-68m9-q2c7

References

Exploit 1

https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2

Advisory 3

Other 1

https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git%3Ba=commit%3Bh=3462280f2e23e16adf3ed5176e0f2413d8861320

TI-2021-12953 Libgcrypt before 1.8.8 and 1.9.x before 1.9.3 mishandles ElGamal encryption because it… CVSS 3.1HIGH 7.5
TI-2017-00354 Information disclosure in libgcrypt CVSS 3.0HIGH 7.5
TI-2017-05168 Information disclosure in GnuPG libgcrypt CVSS 3.0MEDIUM 6.8
TI-2021-02343 _gcry_md_block_write in cipher/hash-common.c in Libgcrypt version 1.9.0 has a heap-based… CVSS 3.1HIGH 7.8
TI-2018-04986 cipher/elgamal.c in Libgcrypt through 1.8.2, when used to encrypt messages directly… CVSS 3.0HIGH 7.5
TI-2019-09661 In Libgcrypt 1.8.4, the C implementation of AES is vulnerable to a flush-and-reload… CVSS 3.1MEDIUM 5.9

See all 16 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences