Amazon Linux 2023 Security Advisory: ALAS2023-2026-1939
Advisory Released Date: 2026-07-20
Advisory Updated Date: 2026-07-20
Severity:
Medium
Issue Overview:
An integer underflow vulnerability was found in MIT krb5 in the berval2tl_data() function in plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c. The function performs an unsigned subtraction (bv_len - 2) without a prior bounds check. When bv_len is 0 or 1, the subtraction wraps to a large value which is then truncated to uint16_t, yielding 0xFFFE (65534) or 0xFFFF (65535). The subsequent malloc succeeds and memcpy reads up to 65534 bytes from a 0-1 byte buffer, resulting in a heap out-of-bounds read.
The attack vector involves a malicious or compromised LDAP KDB backend returning a krbExtraData attribute with bv_len < 2, triggering the underflow when the KDC or kadmind reads principal data. (CVE-2026-11850)
Affected Packages:
krb5
Issue Correction:
Run dnf update krb5 --releasever 2023.12.20260720 or dnf update --advisory ALAS2023-2026-1939 --releasever 2023.12.20260720 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:
libkadm5-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-libs-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-workstation-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-pkinit-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
libkadm5-1.21.3-8.amzn2023.0.1.aarch64
krb5-server-1.21.3-8.amzn2023.0.1.aarch64
krb5-server-ldap-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-pkinit-1.21.3-8.amzn2023.0.1.aarch64
krb5-debugsource-1.21.3-8.amzn2023.0.1.aarch64
krb5-server-ldap-1.21.3-8.amzn2023.0.1.aarch64
krb5-workstation-1.21.3-8.amzn2023.0.1.aarch64
krb5-server-debuginfo-1.21.3-8.amzn2023.0.1.aarch64
krb5-libs-1.21.3-8.amzn2023.0.1.aarch64
krb5-devel-1.21.3-8.amzn2023.0.1.aarch64
src:
krb5-1.21.3-8.amzn2023.0.1.src
x86_64:
krb5-libs-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
libkadm5-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-server-ldap-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-pkinit-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-workstation-1.21.3-8.amzn2023.0.1.x86_64
krb5-server-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-workstation-debuginfo-1.21.3-8.amzn2023.0.1.x86_64
krb5-pkinit-1.21.3-8.amzn2023.0.1.x86_64
krb5-server-ldap-1.21.3-8.amzn2023.0.1.x86_64
krb5-server-1.21.3-8.amzn2023.0.1.x86_64
krb5-devel-1.21.3-8.amzn2023.0.1.x86_64
libkadm5-1.21.3-8.amzn2023.0.1.x86_64
krb5-debugsource-1.21.3-8.amzn2023.0.1.x86_64
krb5-libs-1.21.3-8.amzn2023.0.1.x86_64