CVE-2025-9820 | Gnutls: stack-based buffer overflow in gnutls_pkcs11_token_init() function

A flaw was found in the GnuTLS library, specifically in the gnutls_pkcs11_token_init() function that handles PKCS#11 token initialization. When a token label longer than expected is processed, the function writes past the end of a fixed-size stack buffer. This programming error can cause the application using GnuTLS to crash or, in certain conditions, be exploited for code execution. As a result, systems or applications relying on GnuTLS may be vulnerable to a denial of service or local privilege escalation attacks.

Published: 2026-01-26 Last update: 2026-05-12 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2025-9820 is rated Low Risk (16.2/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Mandatory action: Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-9820

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-01-27 0.01%

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-9820

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.0 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
2.5 1.4 [email protected]

Weakness enumeration for CVE-2025-9820

GitHub Security Advisory for CVE-2025-9820

GHSA-337w-h8w7-m899 · Severity: medium — A flaw was found in the GnuTLS library, specifically in the gnutls_pkcs11_token_init() function...

OS Trackers for CVE-2025-9820

vendor priority summary link
alpine CVE-2025-9820: 1 source package rows (gnutls); 5 state rows across 5 repos (3.20-main, 3.21-main, 3.22-main, 3.23-main, edge-main); fixed 5, open 0. https://security.alpinelinux.org/vuln/CVE-2025-9820
debian not yet assigned CVE-2025-9820 not yet assigned priority: Debian including 1 source packages (gnutls28), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-9820
redhat low https://access.redhat.com/security/cve/CVE-2025-9820
suse medium CVE-2025-9820 severity moderate: SUSE including 301 source package names (0.23.1-11.90:libgnutls30-3.8.3-150600.4.12.1, 0.6.36-13.5:libgnutls30-3.8.3-150600.4.12.1, …), 631 product×package rows across 260 product lines (Container bci/spack, Container containers/open-webui, … (260 product lines)): Fixed 394, Known Affected 231, First Fixed 5, Known Not Affected 1. https://www.suse.com/security/cve/CVE-2025-9820/
ubuntu low CVE-2025-9820 low priority: Ubuntu including 1 source packages (gnutls28), 8 status rows across 8 suites (bionic, focal, jammy, noble, plucky, questing, upstream, xenial): released 4, needs-triage 3, ignored 1. https://ubuntu.com/security/CVE-2025-9820

Affected software / configurations for CVE-2025-9820

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-9820

URL Tags
https://access.redhat.com/errata/RHSA-2026:13812
https://access.redhat.com/errata/RHSA-2026:3477
https://access.redhat.com/errata/RHSA-2026:4188
https://access.redhat.com/errata/RHSA-2026:4655
https://access.redhat.com/errata/RHSA-2026:4943
https://access.redhat.com/errata/RHSA-2026:5585
https://access.redhat.com/errata/RHSA-2026:5606
https://access.redhat.com/errata/RHSA-2026:7329
https://access.redhat.com/errata/RHSA-2026:7477
https://access.redhat.com/security/cve/CVE-2025-9820
https://bugzilla.redhat.com/show_bug.cgi?id=2392528
https://gitlab.com/gnutls/gnutls/-/commit/1d56f96f6ab5034d677136b9d50b5a75dff0faf5
https://gitlab.com/gnutls/gnutls/-/issues/1732
https://www.gnutls.org/security-new.html#GNUTLS-SA-2025-11-18
http://www.openwall.com/lists/oss-security/2025/11/20/2
https://cert-portal.siemens.com/productcert/html/ssa-032379.html
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