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Fencer Vulns
medium 4.5

CVE-2021-3696 json

A heap out-of-bounds write may heppen during the handling of Huffman tables in the PNG reader.

published 2022-07-06 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26981

cvss
4.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

A heap out-of-bounds write may heppen during the handling of Huffman tables in the PNG reader. This may lead to data corruption in the heap space. Confidentiality, Integrity and Availablity impact may be considered Low as it's very complex to an attacker control the encoding and positioning of corrupted Huffman entries to achieve results such as arbitrary code execution and/or secure boot circumvention. This flaw affects grub2 versions prior grub-2.12.

Patch / fix

  • gnu grub2 2.12
  • grub2 Debian 14, Debian 13, Debian 12 2.06-3

debian advisories DEBIAN-CVE-2021-3696

  • grub2-signed Ubuntu 18.04 LTS 1.187.3~18.04.1
  • grub2-signed Ubuntu 20.04 LTS 1.187.3~20.04.1
  • grub2-signed Ubuntu 22.04 LTS 1.187.3~22.04.1
  • grub2-unsigned Ubuntu 22.04 LTS, Ubuntu 20.04 LTS, Ubuntu 18.04 LTS 2.06-2ubuntu14.1

ubuntu advisories UBUNTU-CVE-2021-3696

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • shim-unsigned-x64 RHEL 9 15.6-1.el9
  • shim RHEL 9 15.6-1.el9
  • grub2 RHEL 9 1:2.06-27.el9_0.7
  • grub2-pc RHEL 9 1:2.06-27.el9_0.7
  • shim-x64 RHEL 9 15.6-1.el9
  • shim-aa64 RHEL 9 15.6-1.el9
  • grub2-tools RHEL 9 1:2.06-27.el9_0.7
  • grub2-common RHEL 9 1:2.06-27.el9_0.7

red hat advisories RHSA-2022:5099RHSA-2022:5100RHSA-2022:5095RHSA-2022:5096RHSA-2022:5098

  • grub2 SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLES 15 SP2-BCL +6 more 2.04-150200.9.63.2
  • grub2 SLE Micro 5.1 2.04-150300.3.5.1
  • grub2 SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.2 +2 more 2.04-150300.22.20.2
  • grub2 SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 2.02-150100.123.12.2
  • grub2 SLES 12 SP2-BCL 2.02-115.67.2
  • grub2 SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES 12 SP5 +3 more 2.02-143.2
  • grub2 SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 2.02-137.2
  • grub2 SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 2.02-150000.122.12.2

suse advisories SUSE-SU-2022:2074-1SUSE-SU-2022:2073-1SUSE-SU-2022:2064-1SUSE-SU-2022:2041-1SUSE-SU-2022:2039-1SUSE-SU-2022:2038-1

  • grub2 openSUSE Tumbleweed 2.06-25.1

opensuse advisories openSUSE-SU-2024:12137-1

  • shim-unsigned-x64 AlmaLinux 8 15.6-1.el8.alma
  • grub2-pc AlmaLinux 8 1:2.02-123.el8_6.8.alma
  • shim-x64 AlmaLinux 8 15.6-1.el8.alma
  • shim-aa64 AlmaLinux 8 15.6-1.el8.alma
  • shim-ia32 AlmaLinux 8 15.6-1.el8.alma
  • grub2-tools AlmaLinux 8 1:2.02-123.el8_6.8.alma
  • grub2-common AlmaLinux 8 1:2.02-123.el8_6.8.alma
  • grub2-efi-x64 AlmaLinux 8 1:2.02-123.el8_6.8.alma

almalinux advisories ALSA-2022:5095ALSA-2022:5099

  • shim Rocky Linux 9 15.6-1.el9
  • shim Rocky Linux 9 15.6-1.el9.rocky.0.1
  • mokutil Rocky Linux 9 2:0.4.0-8.el9_0.1
  • shim-unsigned-x64 Rocky Linux 8 15.6-1.el8
  • shim Rocky Linux 8 15.6-1.el8
  • grub2 Rocky Linux 8 1:2.02-123.el8_6.8
  • mokutil Rocky Linux 8 1:0.3.0-11.el8_6.1

rocky linux advisories RLSA-2022:5099RLSA-2022:5095

  • grub2 CBL-Mariner 2.0 2.06-12
  • grub2 Azure Linux 3.0 2.06-14

azure linux advisories AZL-31035AZL-34784

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3696 updated cvss 5.0

grub2: Crafted PNG image may lead to out-of-bound write during huffman table handling

  • Red Hat Enterprise Linux 7 grub2, grub2-pc, grub2-efi, grub2-ppc64, grub2-tools, grub2-common, +15 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux BaseOS (v. 8) grub2 2.02-123.el8_6.8, grub2-pc 2.02-123.el8_6.8, grub2-tools 2.02-123.el8_6.8, grub2-common 2.02-123.el8_6.8, grub2-efi-x64 2.02-123.el8_6.8, grub2-ppc64le 2.02-123.el8_6.8, +13 more
    fixed: vendor fix RHSA-2022:5095
  • Red Hat Enterprise Linux BaseOS (v. 9) grub2 2.06-27.el9_0.7, grub2-pc 2.06-27.el9_0.7, grub2-tools 2.06-27.el9_0.7, grub2-common 2.06-27.el9_0.7, grub2-efi-x64 2.06-27.el9_0.7, grub2-ppc64le 2.06-27.el9_0.7, +10 more
    fixed: vendor fix RHSA-2022:5099
  • Red Hat Enterprise Linux BaseOS E4S (v. 8.1) grub2 2.02-87.el8_1.10, grub2-pc 2.02-87.el8_1.10, grub2-tools 2.02-87.el8_1.10, grub2-common 2.02-87.el8_1.10, grub2-efi-x64 2.02-87.el8_1.10, grub2-ppc64le 2.02-87.el8_1.10, +11 more
    fixed: vendor fix RHSA-2022:5098
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.2) grub2 2.02-87.el8_2.10, grub2-pc 2.02-87.el8_2.10, grub2-tools 2.02-87.el8_2.10, grub2-common 2.02-87.el8_2.10, grub2-efi-x64 2.02-87.el8_2.10, grub2-ppc64le 2.02-87.el8_2.10, +13 more
    fixed: vendor fix RHSA-2022:5100
  • Red Hat Enterprise Linux BaseOS EUS (v.8.4) grub2 2.02-99.el8_4.9, grub2-pc 2.02-99.el8_4.9, grub2-tools 2.02-99.el8_4.9, grub2-common 2.02-99.el8_4.9, grub2-efi-x64 2.02-99.el8_4.9, grub2-ppc64le 2.02-99.el8_4.9, +13 more
    fixed: vendor fix RHSA-2022:5096
  • Red Hat CodeReady Linux Builder (v. 9) shim-unsigned-x64 15.6-1.el9 Red Hat CodeReady Linux Builder EUS (v. 8.2) shim-unsigned-x64 15.6-1.el8 Red Hat Enterprise Linux BaseOS (v. 8) shim 15.6-1.el8, shim-x64 15.6-1.el8, shim-aa64 15.6-1.el8, shim-ia32 15.6-1.el8, mokutil 0.3.0-11.el8_6.1 Red Hat Enterprise Linux BaseOS (v. 9) shim 15.6-1.el9, shim-x64 15.6-1.el9, shim-aa64 15.6-1.el9, mokutil 0.4.0-8.el9_0.1 Red Hat Enterprise Linux BaseOS E4S (v. 8.1) shim 15.6-1.el8, shim-x64 15.6-1.el8, shim-ia32 15.6-1.el8, mokutil 0.3.0-9.el8_1.1 Red Hat Enterprise Linux BaseOS EUS (v. 8.2) shim 15.6-1.el8, shim-x64 15.6-1.el8, shim-aa64 15.6-1.el8, shim-ia32 15.6-1.el8, mokutil 0.3.0-9.el8_2.2
    +3 more products
    Red Hat Enterprise Linux BaseOS EUS (v.8.4) shim 15.6-1.el8, shim-x64 15.6-1.el8, shim-aa64 15.6-1.el8, shim-ia32 15.6-1.el8, mokutil 0.3.0-11.el8_4.1 Red Hat Enterprise Linux CRB (v. 8) shim-unsigned-x64 15.6-1.el8 Red Hat Enterprise Linux CRB EUS (v.8.4) shim-unsigned-x64 15.6-1.el8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 4.5 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
NVD 2.0 6.9 AV:L/AC:M/Au:N/C:C/I:C/A:C

Affected products

  • n/a grub2

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.