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    CVE-2021-40528

    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.

    Published:Jul 20, 2021
    Last Modified:Jun 9, 2025
    EPS:Sep 6, 2021
    EPSS Score:0.00097
    CVSS Score:5.9

    Affected Products

    Vendor
    Gnupg
    Product
    Libgcrypt
    Vendor
    Redhat
    Product
    Enterprise Linux

    Exploits

    https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2

    Related CVEs

    CVE-2026-41990 (CVSS 4) — Libgcrypt before 1.12.2 mishandles Dilithium signing. Writes to a static array lack a bounds check but do not …
    CVE-2026-41989 (CVSS 6.7) — Libgcrypt before 1.12.2 sometimes allows a heap-based buffer overflow and denial of service via crafted ECDH c…
    CVE-2021-33560 (CVSS 7.5) — Libgcrypt before 1.8.8 and 1.9.x before 1.9.3 mishandles ElGamal encryption because it lacks exponent blinding…
    CVE-2021-3345 (CVSS 7.8) — _gcry_md_block_write in cipher/hash-common.c in Libgcrypt version 1.9.0 has a heap-based buffer overflow when …
    CVE-2019-12904 (CVSS 5.9) — In Libgcrypt 1.8.4, the C implementation of AES is vulnerable to a flush-and-reload side-channel attack becaus…
    CVE-2018-0495 (CVSS 4.7) — Libgcrypt before 1.7.10 and 1.8.x before 1.8.3 allows a memory-cache side-channel attack on ECDSA signatures t…
    CVE-2018-6829 (CVSS 7.5) — cipher/elgamal.c in Libgcrypt through 1.8.2, when used to encrypt messages directly, improperly encodes plaint…
    CVE-2017-0379 (CVSS 7.5) — Libgcrypt before 1.8.1 does not properly consider Curve25519 side-channel attacks, which makes it easier for a…
    CVE-2017-7526 (CVSS 6.1) — libgcrypt before version 1.7.8 is vulnerable to a cache side-channel attack resulting into a complete break of…
    CVE-2017-9526 (CVSS 5.9) — In Libgcrypt before 1.7.7, an attacker who learns the EdDSA session key (from side-channel observation during …

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High