# CVE-2026-81665: Corosync: corosync: heap-based buffer overflow in totempg assembly buffer during fragmented message reassembly > A heap-based buffer overflow in Corosync allows network-adjacent attackers to crash the cluster daemon or potentially execute code via crafted multicast messages. - **Severity:** High 7.5 (`CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 4 Sep 2026 - **Updated:** 21 Oct 2026 - **Also known as:** ALSA-2026:67872, ALSA-2026:67873, ALSA-2026:69277, AZL-99888, CLSA-2026-1790008457, CLSA-2026-1790352190, DEBIAN-CVE-2026-81665, GHSA-vj89-2c25-485x, RHSA-2026:67872, RHSA-2026:67873, RHSA-2026:67878, RHSA-2026:67879, RHSA-2026:67880, RHSA-2026:67881, RHSA-2026:68574, RHSA-2026:69277, RHSA-2026:69278, RHSA-2026:69279, RHSA-2026:69280, RLSA-2026:67872, RLSA-2026:67873, RLSA-2026:69277, SUSE-SU-2026:4387-1, UBUNTU-CVE-2026-81665 ## What is CVE-2026-81665? CVE-2026-81665 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description A heap-based buffer overflow was found in Corosync's Totem Process Group (totempg) message reassembly. When processing fragmented multicast messages, the buffer used to reassemble fragments lacks a runtime bounds check in release builds. A network-adjacent attacker able to send crafted multicast protocol messages to the cluster could cause a heap buffer overflow with attacker-controlled data. This can crash the Corosync daemon, causing a denial of service to the entire cluster, and may potentially allow further exploitation given sufficient heap-corruption control. Weakness: CWE-122 (Heap-based Buffer Overflow) ## Which versions are affected by CVE-2026-81665? | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `corosync` | AlmaLinux:10 | All versions | 3.1.10-1.el10_2.2 | | `corosync-vqsim` | AlmaLinux:10 | All versions | 3.1.10-1.el10_2.2 | | `corosynclib` | AlmaLinux:10 | All versions | 3.1.10-1.el10_2.2 | | `corosynclib-devel` | AlmaLinux:10 | All versions | 3.1.10-1.el10_2.2 | | `corosync` | AlmaLinux:8 | All versions | 3.1.8-1.el8_10.2 | | `corosync-vqsim` | AlmaLinux:8 | All versions | 3.1.8-1.el8_10.2 | | `corosynclib` | AlmaLinux:8 | All versions | 3.1.8-1.el8_10.2 | | `corosynclib-devel` | AlmaLinux:8 | All versions | 3.1.8-1.el8_10.2 | | `spausedd` | AlmaLinux:8 | All versions | 3.1.8-1.el8_10.2 | | `corosync` | AlmaLinux:9 | All versions | 3.1.10-1.el9_8.2 | | `corosync-vqsim` | AlmaLinux:9 | All versions | 3.1.10-1.el9_8.2 | | `corosynclib` | AlmaLinux:9 | All versions | 3.1.10-1.el9_8.2 | | `corosynclib-devel` | AlmaLinux:9 | All versions | 3.1.10-1.el9_8.2 | | `corosync` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosync-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosync-debugsource` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosync-vqsim` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosync-vqsim-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosynclib` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosynclib-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosynclib-devel` | Red Hat:enterprise_linux:10.2 | All versions | 0:3.1.10-1.el10_2.2 | | `corosync` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosync-debuginfo` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosync-qdevice` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosync-qnetd` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosynclib` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosynclib-devel` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `spausedd` | Red Hat:enterprise_linux:7::server | All versions | 0:2.4.5-7.el7_9.4 | | `corosync` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-vqsim-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosynclib` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosynclib-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `spausedd-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-debugsource` | Red Hat:enterprise_linux:8::crb | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-vqsim` | Red Hat:enterprise_linux:8::crb | All versions | 0:3.1.8-1.el8_10.2 | | `corosync-vqsim-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:3.1.8-1.el8_10.2 | | `corosynclib-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:3.1.8-1.el8_10.2 | ## How do I fix CVE-2026-81665? Apply the vendor's patch. ## Is CVE-2026-81665 being exploited? There is no known exploitation of CVE-2026-81665 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-81665 and fix it if it is affected. What it is: CVE-2026-81665 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-81665 in the wild and no public exploit code. Affected product: Red Hat Enterprise Linux 10. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-81665/ (Markdown: https://insights.sbomify.com/CVE-2026-81665/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81665 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81665 - OSV: https://osv.dev/vulnerability/CVE-2026-81665 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-81665/ Summaries are generated and may contain mistakes; the official description above is the record.