# CVE-2026-23472: serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN CVE-2026-23472 is fixed in 33 products on 1 platform, first by DEBIAN-CVE-2026-23472, released April 3, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-23472 - Priority: Routine - CVSS: 5.5 (Moderate) - EPSS: 0.0016 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Apr 3, 2026 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23472 ## Description In the Linux kernel, the following vulnerability has been resolved: serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN uart_write_room() and uart_write() behave inconsistently when xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were never properly initialized): - uart_write_room() returns kfifo_avail() which can be > 0 - uart_write() checks xmit_buf and returns 0 if NULL This inconsistency causes an infinite loop in drivers that rely on tty_write_room() to determine if they can write: while (tty_write_room(tty) > 0) { written = tty->ops->write(...); // written is always 0, loop never exits } For example, caif_serial's handle_tx() enters an infinite loop when used with PORT_UNKNOWN serial ports, causing system hangs. Fix by making uart_write_room() also check xmit_buf and return 0 if it's NULL, consistent with uart_write(). Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13 ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bpftool6.18 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | bpftool6.18-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel-64kb sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-azure sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default-base sles 15.7 | 6.4.0-150700.53.55.1.150700.17.33.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-docs sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-livepatch-6.18.20-20.229 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel-livepatch-SLE15-SP7_Update_15 sles 15.7 | 1-150700.15.3.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-obs-build sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-source sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-syms sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-zfcpdump sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel6.18 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-debuginfo-common-aarch64 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-debuginfo-common-x86_64 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-devel amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-headers amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-libbpf amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-libbpf-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-libbpf-devel amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-libbpf-static amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-modules-extra amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-modules-extra-common amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-tools amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-tools-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | kernel6.18-tools-devel amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-23472](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23472.md) | Apr 3, 2026 | | Linux | linux Debian 14 | 6.19.10-1 | [DEBIAN-CVE-2026-23472](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23472.md) | Apr 3, 2026 | | Linux | perf6.18 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | perf6.18-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | python3-perf6.18 amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | | Linux | python3-perf6.18-debuginfo amzn 2023 | 1:6.18.20-20.229.amzn2023 | [ALAS2023-2026-1596](https://patchblox.com/security/data/fix/linux/alas2023-2026-1596.md) | Apr 27, 2026 | --- Data as of 2026-11-08T13:06:02Z UTC. 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