# CVE-2021-33560: Libgcrypt before 1.8.8 and 1.9.x before 1.9.3 mishandles ElGamal encryption because it lacks exponent blinding to address a side-channel attack against mpi_powm and the window size is not chosen appropriately. This for example affects use of ElGamal in OpenPGP.

CVE-2021-33560 is fixed in 4 products on 1 platform, first by libgcrypt20 1.8.1-4ubuntu1.3, released September 6, 2021. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-33560
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0237
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 8, 2021
- Weakness: Observable Discrepancy
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33560

## Description

Libgcrypt before 1.8.8 and 1.9.x before 1.9.3 mishandles ElGamal encryptionbecause it lacks exponent blinding to address a side-channel attack againstmpi_powm, and the window size is not chosen appropriately. This, forexample, affects use of ElGamal in OpenPGP.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libgcrypt RHEL 8 | 0:1.8.5-6.el8 | [RHSA-2021:4409](https://patchblox.com/security/data/fix/linux/rhsa-2021-4409.md) | Nov 9, 2021 |
| Linux | libgcrypt almalinux 8 | 1.8.5-6.el8 | [ALSA-2021:4409](https://patchblox.com/security/data/fix/linux/alsa-2021-4409.md) | Nov 9, 2021 |
| Linux | libgcrypt ol 8 | 0:1.8.5-6.el8 | [ELSA-2021-4409](https://patchblox.com/security/data/fix/linux/elsa-2021-4409.md) | Nov 16, 2021 |
| Linux | libgcrypt rocky 8 | 0:1.8.5-6.el8 | [RLSA-2021:4409](https://patchblox.com/security/data/fix/linux/rlsa-2021-4409.md) | Nov 9, 2021 |
| Linux | libgcrypt-bin Ubuntu 25.04 (plucky) | 1.8.7-5ubuntu2 | [libgcrypt-bin 1.8.7-5ubuntu2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-libgcrypt-bin-1.8.7-5ubuntu2.md) | Jan 16, 2026 |
| Linux | libgcrypt-devel RHEL 8 | 0:1.8.5-6.el8 | [RHSA-2021:4409](https://patchblox.com/security/data/fix/linux/rhsa-2021-4409.md) | Nov 9, 2021 |
| Linux | libgcrypt-devel almalinux 8 | 1.8.5-6.el8 | [ALSA-2021:4409](https://patchblox.com/security/data/fix/linux/alsa-2021-4409.md) | Nov 9, 2021 |
| Linux | libgcrypt-devel ol 8 | 0:1.8.5-6.el8 | [ELSA-2021-4409](https://patchblox.com/security/data/fix/linux/elsa-2021-4409.md) | Nov 16, 2021 |
| Linux | libgcrypt20 Ubuntu 18.04.6 LTS (bionic) | 1.8.1-4ubuntu1.3 | [libgcrypt20 1.8.1-4ubuntu1.3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libgcrypt20-1.8.1-4ubuntu1.3.md) | Sep 6, 2021 |
| Linux | libgcrypt20 Ubuntu 20.04 LTS (focal) | 1.8.5-5ubuntu1.1 | [libgcrypt20 1.8.5-5ubuntu1.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libgcrypt20-1.8.5-5ubuntu1.1.md) | Sep 6, 2021 |
| Linux | libgcrypt20 Ubuntu 22.04.1 LTS (jammy) | 1.8.7-5ubuntu2 | [libgcrypt20 1.8.7-5ubuntu2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libgcrypt20-1.8.7-5ubuntu2.md) | Sep 6, 2021 |
| Linux | libgcrypt20 Ubuntu 24.10 (oracular) | 1.8.7-5ubuntu2 | [libgcrypt20 1.8.7-5ubuntu2](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-libgcrypt20-1.8.7-5ubuntu2.md) | Jan 16, 2026 |
| Linux | libgcrypt20 Ubuntu 25.04 (plucky) | 1.8.7-5ubuntu2 | [libgcrypt20 1.8.7-5ubuntu2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-libgcrypt20-1.8.7-5ubuntu2.md) | Jan 16, 2026 |

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