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Fencer Vulns
medium 5.9

CVE-2021-40528 json

The ElGamal implementation in Libgcrypt before 1.9.4 allows plaintext recovery because, during interaction between two cryptographic librar…

published 2021-09-06 5 y ago modified 2026-07-18 3 mo ago also EUVD-2021-27703 , JLSEC-2026-124

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.4%
EPSS 1.4% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

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.

Patch / fix

  • julia Libgcrypt_jll 1.11.0+0
  • gnupg libgcrypt 1.9.4
  • libgcrypt20 Debian 14, Debian 13, Debian 12 1.8.7-6

debian advisories DEBIAN-CVE-2021-40528

  • libgcrypt20 Ubuntu 18.04 LTS 1.8.1-4ubuntu1.3
  • libgcrypt20 Ubuntu 20.04 LTS 1.8.5-5ubuntu1.1
  • libgcrypt20 Ubuntu 22.04 LTS 1.8.7-5ubuntu2
  • libgcrypt20 Ubuntu Pro 16.04 LTS 1.6.5-2ubuntu0.6+esm1
  • libgcrypt20 Ubuntu Pro FIPS-updates 18.04 LTS 1.8.1-4ubuntu1.fips.3
  • libgcrypt20 Ubuntu Pro FIPS-updates 20.04 LTS, Ubuntu Pro FIPS 20.04 LTS 1.8.5-5ubuntu1.fips.1.1

ubuntu advisories UBUNTU-CVE-2021-40528

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libgcrypt RHEL 8 1.8.5-7.el8_6

red hat advisories RHSA-2022:5311

  • libgcrypt openSUSE Tumbleweed 1.10.1-1.1

opensuse advisories openSUSE-SU-2024:12540-1

  • libgcrypt AlmaLinux 8 1.8.5-7.el8_6

almalinux advisories ALSA-2022:5311

  • libgcrypt Rocky Linux 8 1.8.5-7.el8_6

rocky linux advisories RLSA-2022:5311

  • libgcrypt Alpine 3.13, Alpine 3.12, Alpine 3.11 1.8.8-r1

alpine advisories ALPINE-CVE-2021-40528

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-40528 updated cvss 5.9

libgcrypt: ElGamal implementation allows plaintext recovery

  • Red Hat Enterprise Linux 6 libgcrypt Red Hat Enterprise Linux 7 libgcrypt
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux BaseOS (v. 8) libgcrypt 1.8.5-7.el8_6
    fixed: vendor fix RHSA-2022:5311
  • Red Hat Enterprise Linux 9 libgcrypt
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
17 mo ago

Exploit prediction

1.42% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • ibm.github.io https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 2.6 AV:N/AC:H/Au:N/C:P/I:N/A:N
OSV 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia Libgcrypt_jll
<1.11.0+0
1.11.0+0

Classification

Weakness
  • CWE-327 Use of a Broken or Risky Cryptographic Algorithm

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.