# CVE-2021-20254: Information disclosure in samba > A flaw in Samba's group mapping allows reading beyond array bounds, potentially exposing or modifying user group membership data. - **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N`) - **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:** 5 May 2021 - **Updated:** 3 Aug 2024 - **Also known as:** ALPINE-CVE-2021-20254, ALSA-2021:4058, AZL-36999, AZL-7352, DEBIAN-CVE-2021-20254, ECHO-3f66-59c9-67b2, GHSA-3r9x-25h6-9v89, RHSA-2021:2313, RHSA-2021:3724, RHSA-2021:3988, RHSA-2021:4058, RHSA-2021:4866, RLSA-2021:4058, SUSE-SU-2021:1438-1, SUSE-SU-2021:1439-1, SUSE-SU-2021:1442-1, SUSE-SU-2021:1445-1, SUSE-SU-2021:14709-1, SUSE-SU-2021:1492-1, UBUNTU-CVE-2021-20254, USN-4930-1 ## What is CVE-2021-20254? CVE-2021-20254 is a medium-severity vulnerability in Debian Debian Linux, published on 5 May 2021. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description A flaw was found in samba. The Samba smbd file server must map Windows group identities (SIDs) into unix group ids (gids). The code that performs this had a flaw that could allow it to read data beyond the end of the array in the case where a negative cache entry had been added to the mapping cache. This could cause the calling code to return those values into the process token that stores the group membership for a user. The highest threat from this vulnerability is to data confidentiality and integrity. Weakness: CWE-125 (Out-of-bounds Read) ## Which versions are affected by CVE-2021-20254? It affects 4 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `libsmbclient-devel` | AlmaLinux:8 | All versions | 4.13.3-5.el8_4 | | `libwbclient-devel` | AlmaLinux:8 | All versions | 4.13.3-5.el8_4 | | `samba-devel` | AlmaLinux:8 | All versions | 4.13.3-5.el8_4 | | `libsmbclient` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `libsmbclient-devel` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `libwbclient` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `libwbclient-devel` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-client` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-client-libs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-common` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-common-libs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-common-tools` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-dc` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-dc-libs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-debuginfo` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-devel` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-krb5-printing` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-libs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-pidl` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-python` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-python-test` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-test` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-test-libs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-vfs-glusterfs` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-winbind` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-winbind-clients` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-winbind-krb5-locator` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `samba-winbind-modules` | Red Hat:enterprise_linux:7::client | All versions | 0:4.10.16-15.el7_9 | | `libsmbclient-devel` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `libwbclient-devel` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-dc` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-dc-libs` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-debuginfo` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-devel` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-krb5-printing` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-pidl` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-python` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | | `samba-python-test` | Red Hat:enterprise_linux:7::computenode | All versions | 0:4.10.16-15.el7_9 | Products: Debian Debian Linux, Fedoraproject Fedora, Redhat Enterprise Linux, Samba Samba. ## How do I fix CVE-2021-20254? Apply the vendor's patch. ## Is CVE-2021-20254 being exploited? There is no known exploitation of CVE-2021-20254 in the wild and no public exploit code. ## Other vulnerabilities in Debian Debian Linux - [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild) - [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild) - [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild) - [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild) - [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-20254 and fix it if it is affected. What it is: CVE-2021-20254 is a medium-severity vulnerability in Debian Debian Linux, published on 5 May 2021. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-20254 in the wild and no public exploit code. Affected product: Debian Debian Linux. 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-2021-20254/ (Markdown: https://insights.sbomify.com/CVE-2021-20254/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20254 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20254 - OSV: https://osv.dev/vulnerability/CVE-2021-20254 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-20254/ Summaries are generated and may contain mistakes; the official description above is the record.