# CVE-2026-87853: Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation > Attackers can impersonate other users by exploiting a prefix comparison flaw in SSSD's OIDC authentication, leading to unauthorized access. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 9 Sep 2026 - **Updated:** 29 Oct 2026 - **Also known as:** ALSA-2026:77534, DEBIAN-CVE-2026-87853, GHSA-993g-jgf7-rg3x, RHSA-2026:77534, RLSA-2026:77534, UBUNTU-CVE-2026-87853, openSUSE-SU-2026:11825-1 ## What is CVE-2026-87853? CVE-2026-87853 is a high-severity authentication bypass vulnerability in Red Hat Enterprise Linux 10, published on 9 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description A flaw was found in SSSD's IdP authentication provider. The eval_access_token_buf() function compares the OIDC subject identifier using strncmp() with the authenticated user's identifier length, performing a prefix comparison instead of an exact match. An attacker whose IdP identifier is a strict prefix of a target user's identifier can authenticate as the target user. Weakness: CWE-187 (Partial String Comparison) ## Which versions are affected by CVE-2026-87853? | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `libipa_hbac` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_autofs` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_certmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_idmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_nss_idmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_nss_idmap-devel` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libsss_sudo` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `python3-libipa_hbac` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `python3-libsss_nss_idmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `python3-sss` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `python3-sss-murmur` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `python3-sssdconfig` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-ad` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-client` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-common` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-common-pac` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-dbus` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-idp` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-ipa` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-kcm` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-krb5` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-krb5-common` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-ldap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-nfs-idmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-passkey` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-proxy` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-tools` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `sssd-winbind-idmap` | AlmaLinux:10 | All versions | 2.12.0-3.el10_2.2 | | `libipa_hbac` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libipa_hbac-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_autofs` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_autofs-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_certmap` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_certmap-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_idmap` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_idmap-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_nss_idmap` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_nss_idmap-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | | `libsss_nss_idmap-devel` | Red Hat:enterprise_linux:10.2 | All versions | 0:2.12.0-3.el10_2.2 | ## How do I fix CVE-2026-87853? Apply the vendor's patch. ## Is CVE-2026-87853 being exploited? There is no known exploitation of CVE-2026-87853 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-87853 and fix it if it is affected. What it is: CVE-2026-87853 is a high-severity authentication bypass vulnerability in Red Hat Enterprise Linux 10, published on 9 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-87853 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-2026-87853/ (Markdown: https://insights.sbomify.com/CVE-2026-87853/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87853 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87853 - OSV: https://osv.dev/vulnerability/CVE-2026-87853 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-87853/ Summaries are generated and may contain mistakes; the official description above is the record.