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CVE-2021-40528

22
FAUCET Score

CVE-2021-40528 describes a plaintext recovery vulnerability in the ElGamal implementation of Libgcrypt versions prior to 1.9.4, impacting products like GnuPG. This medium-severity flaw (CVSS 5.9) allows an attacker to recover plaintext due to a dangerous combination of cryptographic parameters during cross-library interaction, specifically affecting OpenPGP. While the attack complexity is high, successful exploitation could lead to complete confidentiality compromise. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.9.4CPE matchmatch criteria
cpe:2.3:a:gnupg:libgcrypt:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.9MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.42%
Probability of exploitation in next 30 days
EPSS Percentile
70.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0142 is in the 41st percentile among its peer group of 19,956 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

microsoftpatch availablevia msrc
Product: 18997-16820Fixed in: 1.8.7-3
microsoftpatch availablevia msrc
Product: cm1 libgcrypt 1.8.7-3 on CBL Mariner 1.0Fixed in: 1.8.7-3
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: libgcrypt-0:1.8.5-7.el8_6
View patch

Vendor Advisories (2)

microsoft2021-Sep/CVE-2021-40528Moderate

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.

Sep 14, 2021
redhatCVE-2021-40528Moderate

libgcrypt: ElGamal implementation allows plaintext recovery

Jul 20, 2021

References

eprint.iacr.org / 2021/923
Technical DescriptionThird Party Advisory
git.gnupg.org / cgi-bin/gitweb.cgi
ibm.github.io / system-security-research-updates/2021/07/20/insecurity-elgamal-pt1
Third Party Advisory
ibm.github.io / system-security-research-updates/2021/09/06/insecurity-elgamal-pt2
ExploitThird Party Advisory
security.gentoo.org / glsa/202210-13
Third Party Advisory