ALAS2023-2026-2039

References: CVE-2026-12413  CVE-2026-50721  CVE-2026-50722 
FAQs regarding Amazon Linux ALAS/CVE Severity

Issue Overview:

An invalidly formatted IKEv2 fragment causes the Libreswan pluto daemon to crash and restart. Continued exploitation would cause a denial of service. The function reassemble_v2_incoming_fragments() would ignore unknown outer payloads but still store these in a fixed size array msg_digest.digest[PAYLIMIT]. An off-by-one error in the assertion PASSERT(logger, md->digest_roof < elemsof(md->digest)) causes the daemon to abort. No remote code execution is possible. Any configuration that allows IKEv2 connections that do not set fragmentation=no are vulnerable. IKEv1 is not affected. (CVE-2026-12413)

Libreswan, via the function RSA_authenticate_hash_signature_raw_rsa(), did not correctly verify the length of the authentication hash when the SIG payload of an IKEv1 packet was encoded using PKCS #1 RSA Encryption as per RFC 2313. A remote attacker can use a variation on the Bleichenbacher attack to forge the SIG payload when small public exponents are being used (e.g., e=3), which could lead to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the SIG payload, could trigger an assertion leading to denial-of-service. The daemon aborts and restarts; continued exploitation causes sustained denial of service. Remote code execution is not possible. X.509 certificate verifications of remote IKE peers are not affected. (CVE-2026-50721)

Libreswan, via the function RSA_authenticate_hash_signature_pkcs1_1_5_rsa(), did not correctly verify the DER encoding of the ASN.1 digest when the IKEv2 AUTH payload was encoded using RSASSA-PKCS1-v1_5 (RFC 8017). A remote attacker can use a variation on the Bleichenbacher attack to forge the AUTH payload when small public exponents are used (e.g., e=3), leading to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the AUTH payload, could trigger an assertion leading to denial-of-service. The daemon aborts and restarts; continued exploitation causes sustained denial of service. Remote code execution is not possible. X.509 certificate verifications of the remote IKE peer are not affected. (CVE-2026-50722)

Issue Correction:
Run dnf update libreswan --releasever 2023.12.20260803 or dnf update --advisory ALAS2023-2026-2039 --releasever 2023.12.20260803 to update your system.
More information on how to update your system can be found on this page: Amazon Linux 2023 documentation

New Packages:

aarch64:
    libreswan-debuginfo-4.12-3.amzn2023.0.3.aarch64
    libreswan-4.12-3.amzn2023.0.3.aarch64
    libreswan-debugsource-4.12-3.amzn2023.0.3.aarch64

src:
    libreswan-4.12-3.amzn2023.0.3.src

x86_64:
    libreswan-debuginfo-4.12-3.amzn2023.0.3.x86_64
    libreswan-4.12-3.amzn2023.0.3.x86_64
    libreswan-debugsource-4.12-3.amzn2023.0.3.x86_64