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Critical · 9.8 CVE-2026-63886 EUVD-2026-45771GHSA-f9cg-2c9v-xhmh

scsi: target: iscsi: Validate CHAP_R length before base64 decode

Published Jul 19, 2026 · Updated Oct 19, 2026 · Assigned by Linux

Vendor: Linux Product: Linux Package: linux Package: linux Package: linux-allwinner-5.19 Package: linux-aws Package: linux-aws-5.0 Package: linux-aws-5.11 Package: linux-aws-5.13 Package: linux-aws-5.19 Package: linux-aws-5.3 Package: linux-aws-5.8 Package: linux-aws-6.14 Package: linux-aws-6.17 Package: linux-aws-6.2 Package: linux-aws-6.5 Package: linux-aws-6.8 Package: linux-aws-fips Package: linux-azure Package: linux-azure-5.11 Package: linux-azure-5.13 Package: linux-azure-5.19 Package: linux-azure-5.3 Package: linux-azure-5.8 Package: linux-azure-6.11 Package: linux-azure-6.14 Package: linux-azure-6.17 Package: linux-azure-6.2 Package: linux-azure-6.5 Package: linux-azure-6.8 Package: linux-azure-7.0 Package: linux-azure-edge Package: linux-azure-fde Package: linux-azure-fde-5.19 Package: linux-azure-fde-6.14 Package: linux-azure-fde-6.17 Package: linux-azure-fde-6.2 Package: linux-azure-fde-6.8 Package: linux-azure-fde-7.0 Package: linux-azure-fips Package: linux-azure-nvidia Package: linux-azure-nvidia-6.14 Package: linux-bluefield Package: linux-fips Package: linux-gcp Package: linux-gcp-5.11 Package: linux-gcp-5.13 Package: linux-gcp-5.19 Package: linux-gcp-5.3 Package: linux-gcp-5.8 Package: linux-gcp-6.11 Package: linux-gcp-6.14 Package: linux-gcp-6.17 Package: linux-gcp-6.2 Package: linux-gcp-6.5 Package: linux-gcp-6.8 Package: linux-gcp-7.0 Package: linux-gcp-fips Package: linux-gke Package: linux-gke-4.15 Package: linux-gke-5.15 Package: linux-gke-5.4 Package: linux-gkeop Package: linux-gkeop-5.15 Package: linux-gkeop-5.4 Package: linux-hwe Package: linux-hwe-5.11 Package: linux-hwe-5.13 Package: linux-hwe-5.19 Package: linux-hwe-5.8 Package: linux-hwe-6.11 Package: linux-hwe-6.14 Package: linux-hwe-6.17 Package: linux-hwe-6.2 Package: linux-hwe-6.5 Package: linux-hwe-6.8 Package: linux-hwe-7.0 Package: linux-hwe-edge Package: linux-ibm Package: linux-ibm-6.8 Package: linux-intel-5.13 Package: linux-intel-iot-realtime Package: linux-lowlatency Package: linux-lowlatency-hwe-5.19 Package: linux-lowlatency-hwe-6.11 Package: linux-lowlatency-hwe-6.2 Package: linux-lowlatency-hwe-6.5 Package: linux-lowlatency-hwe-6.8 Package: linux-nvidia Package: linux-nvidia-6.11 Package: linux-nvidia-6.17 Package: linux-nvidia-6.2 Package: linux-nvidia-6.5 Package: linux-nvidia-6.8 Package: linux-nvidia-7.0 Package: linux-nvidia-bos Package: linux-nvidia-lowlatency Package: linux-nvidia-tegra Package: linux-oem Package: linux-oem-5.10 Package: linux-oem-5.13 Package: linux-oem-5.14 Package: linux-oem-5.17 Package: linux-oem-5.6 Package: linux-oem-6.0 Package: linux-oem-6.1 Package: linux-oem-6.11 Package: linux-oem-6.14 Package: linux-oem-6.17 Package: linux-oem-6.5 Package: linux-oem-6.8 Package: linux-oem-7.0 Package: linux-oracle Package: linux-oracle-5.0 Package: linux-oracle-5.11 Package: linux-oracle-5.13 Package: linux-oracle-5.3 Package: linux-oracle-5.8 Package: linux-oracle-6.14 Package: linux-oracle-6.17 Package: linux-oracle-6.5 Package: linux-oracle-6.8 Package: linux-oracle-7.0 Package: linux-raspi Package: linux-raspi-realtime Package: linux-raspi2 Package: linux-realtime Package: linux-realtime-6.14 Package: linux-realtime-6.17 Package: linux-realtime-6.8 Package: linux-riscv Package: linux-riscv-5.11 Package: linux-riscv-5.19 Package: linux-riscv-5.8 Package: linux-riscv-6.14 Package: linux-riscv-6.17 Package: linux-riscv-6.5 Package: linux-riscv-6.8 Package: linux-riscv-7.0 Package: linux-starfive-5.19 Package: linux-starfive-6.2 Package: linux-starfive-6.5 Package: linux-vmware Package: linux-xilinx Platform: Linux Ecosystem: Debian Ecosystem: Ubuntu

Description

In the Linux kernel, the following vulnerability has been resolved:

scsi: target: iscsi: Validate CHAP_R length before base64 decode

chap_server_compute_hash() allocates client_digest as
kzalloc(chap->digest_size) and then, for BASE64-encoded responses,
passes chap_r directly to chap_base64_decode() without checking whether
the input length could produce more than digest_size bytes of output.

chap_base64_decode() writes to the destination unconditionally as long
as there is input to consume. With MAX_RESPONSE_LENGTH set to 128 and
the "0b" prefix stripped by extract_param(), up to 127 base64 characters
can reach the decoder. 127 characters decode to 95 bytes. For SHA-256
(digest_size=32) this overflows client_digest by 63 bytes; for MD5
(digest_size=16) the overflow is 79 bytes.

The length check at line 344 fires after the write has already happened.

The HEX branch in the same switch statement already validates the length
up front. Apply the same approach to the BASE64 branch: strip trailing
base64 padding characters, then reject any input whose data length
exceeds DIV_ROUND_UP(digest_size * 4, 3) before calling the decoder.

Stripping trailing '=' before the comparison handles both padded and
unpadded encodings. chap_base64_decode() already returns early on '=',
so the full original string is still passed to the decoder unchanged.

The mutual CHAP path decodes CHAP_C into initiatorchg_binhex, which is
kzalloc(CHAP_CHALLENGE_STR_LEN). extract_param() caps initiatorchg at
CHAP_CHALLENGE_STR_LEN characters, so at most CHAP_CHALLENGE_STR_LEN-1
base64 characters reach the decoder. The maximum decoded size,
DIV_ROUND_UP((CHAP_CHALLENGE_STR_LEN-1) * 3, 4), is less than
CHAP_CHALLENGE_STR_LEN, so no overflow is possible there. A comment is
added at the call site to document this.

Affected products

VendorProductAffectedFixed
Linux Linux 6.0 6.1.176

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

ReleasePackageFixed inAdvisory
Debian 14 linux 7.0.12-1 —
Debian 13 linux 6.12.94-1 —
Debian 12 linux 6.1.176-1 —
ReleasePackageFixed inAdvisory
Ubuntu Nvidia-BlueField 24.04 LTS linux-bluefield 6.8.0-1031.36 —
Ubuntu 26.04 LTS linux 7.0.0-28.28 —
Ubuntu 26.04 LTS linux-aws +2 7.0.0-1009.9 USN-8618-1, USN-8603-1
Ubuntu 26.04 LTS linux-gcp +1 7.0.0-1008.8 USN-8593-1
Ubuntu 26.04 LTS linux-gke 7.0.0-1003.4 —
Ubuntu 26.04 LTS linux-ibm +1 7.0.0-1010.10 USN-8603-1, USN-8593-1
Ubuntu 26.04 LTS linux-nvidia 7.0.0-1016.16 USN-8663-1
Ubuntu 26.04 LTS linux-nvidia-bos 7.0.0-2016.16 USN-8664-1
Ubuntu 26.04 LTS linux-raspi 7.0.0-1015.15 USN-8618-1
Ubuntu 26.04 LTS linux-riscv +1 7.0.0-28.28.1 —
Ubuntu 24.04 LTS linux 6.8.0-142.142 USN-8817-1
Ubuntu 24.04 LTS linux-aws 6.8.0-1065.68 USN-8817-3
Ubuntu 24.04 LTS linux-azure 6.8.0-1068.76 USN-8817-1
Ubuntu 24.04 LTS linux-azure-7.0 7.0.0-1014.14~24.04.1 USN-8728-2
Ubuntu 24.04 LTS linux-azure-fde 6.8.0-1066.73 USN-8817-1
Ubuntu 24.04 LTS linux-azure-fde-7.0 7.0.0-1013.13~24.04.1 —
Ubuntu 24.04 LTS linux-gcp 6.8.0-1069.77 USN-8817-1
Ubuntu 24.04 LTS linux-gcp-7.0 +1 7.0.0-1011.11~24.04.1 USN-8728-3, USN-8728-1
Ubuntu 24.04 LTS linux-gke 6.8.0-1064.72 USN-8817-1
Ubuntu 24.04 LTS linux-gkeop 6.8.0-1050.54 USN-8817-1
Ubuntu 24.04 LTS linux-hwe-7.0 7.0.0-28.28~24.04.1 —
Ubuntu 24.04 LTS linux-ibm 6.8.0-1065.66 USN-8817-1
Ubuntu 24.04 LTS linux-lowlatency 6.8.0-142.142.1 USN-8817-1
Ubuntu 24.04 LTS linux-nvidia 6.8.0-1063.66 USN-8842-1
Ubuntu 24.04 LTS linux-nvidia-7.0 7.0.0-1016.16~24.04.1 USN-8663-1
Ubuntu 24.04 LTS linux-nvidia-lowlatency 6.8.0-1063.66.1 USN-8842-1
Ubuntu 24.04 LTS linux-nvidia-tegra 6.8.0-1035.38 USN-8781-1
Ubuntu 24.04 LTS linux-oracle 6.8.0-1062.65 USN-8817-1
Ubuntu 24.04 LTS linux-raspi 6.8.0-1065.69 USN-8817-1
Ubuntu 24.04 LTS linux-riscv +29 No fix yet —
Ubuntu 24.04 LTS linux-riscv-7.0 7.0.0-28.28.1~24.04.3 —
Ubuntu 24.04 LTS linux-vmware 6.8.0-1008.8 —
Ubuntu 22.04 LTS linux-aws-6.8 6.8.0-1065.68~22.04.1 USN-8817-3
Ubuntu 22.04 LTS linux-azure-6.8 6.8.0-1068.76~22.04.1 USN-8817-1
Ubuntu 22.04 LTS linux-azure-fde-6.8 6.8.0-1066.73~22.04.1 USN-8817-1
Ubuntu 22.04 LTS linux-gcp-6.8 6.8.0-1069.77~22.04.1 USN-8817-1
Ubuntu 22.04 LTS linux-hwe-6.8 6.8.0-149.149~22.04.1 USN-9066-1
Ubuntu 22.04 LTS linux-ibm-6.8 6.8.0-1066.67~22.04.1 USN-8906-1
Ubuntu 22.04 LTS linux-lowlatency-hwe-6.8 6.8.0-142.142.1~22.04.1 USN-8817-1
Ubuntu 22.04 LTS linux-nvidia-6.8 6.8.0-1063.66~22.04.1 USN-8842-1
Ubuntu 22.04 LTS linux-oracle-6.8 6.8.0-1062.65~22.04.1 USN-8817-1
Ubuntu 22.04 LTS linux-riscv +32 No fix yet —
Ubuntu 22.04 LTS linux-riscv-6.8 6.8.0-142.142~22.04.1 —
Ubuntu 20.04 LTS linux-gke +28 No fix yet —
Show 5 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Ubuntu 18.04 LTS linux-gcp +14 No fix yet —
Ubuntu 16.04 LTS linux-hwe-edge No fix yet —
Ubuntu Pro Realtime 24.04 LTS linux-raspi-realtime 6.8.0-2054.56 USN-8817-1
Ubuntu Pro Realtime 24.04 LTS linux-realtime 6.8.1-1060.61 USN-8817-1
Ubuntu Pro Realtime 24.04 LTS linux-realtime-6.14 +1 No fix yet —
Ubuntu Pro Realtime 22.04 LTS linux-realtime-6.8 6.8.1-1060.61~22.04.1 USN-8817-1
Ubuntu Pro FIPS-updates 24.04 LTS linux-aws-fips 6.8.0-1065.68+fips1 USN-8817-2
Ubuntu Pro FIPS-updates 24.04 LTS linux-fips 6.8.0-142.142+fips1 USN-8817-1
Ubuntu Pro FIPS-updates 24.04 LTS linux-gcp-fips +1 6.8.0-1068.76+fips1 USN-8817-1
ReleasePackageFixed inAdvisory
RHEL 10 rv +76 6.12.0-211.49.1.el10_2 RHSA-2026:57251
RHEL 9 rv +75 5.14.0-687.44.1.el9_8 RHSA-2026:63129
RHEL 8 kernel-rt +12 4.18.0-553.158.1.rt7.499.el8_10 RHSA-2026:59737
RHEL 8 perf +26 4.18.0-553.158.1.el8_10 RHSA-2026:59821
Show 4 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
RHEL 10.0 EUS rv +77 6.12.0-55.103.1.el10_0 RHSA-2026:64767
RHEL 9.6 EUS rv +77 5.14.0-570.140.1.el9_6 RHSA-2026:65708
RHEL 9.4 E4S bpftool 7.3.0-427.149.1.el9_4 RHSA-2026:65712
RHEL 9.4 E4S rv +62 5.14.0-427.149.1.el9_4 RHSA-2026:65712
RHEL 9.2 E4S bpftool 7.0.0-284.191.1.el9_2 RHSA-2026:67723
RHEL 9.2 E4S kernel-rt +14 5.14.0-284.191.1.rt14.476.el9_2 RHSA-2026:67721
RHEL 9.2 E4S perf +47 5.14.0-284.191.1.el9_2 RHSA-2026:67723

AlmaLinux

Errata ↗
ReleasePackageFixed inAdvisory
AlmaLinux 10 rv +74 6.12.0-211.49.1.el10_2 ALSA-2026:57251
AlmaLinux 9 rv +73 5.14.0-687.44.1.el9_8 ALSA-2026:63129
AlmaLinux 8 kernel-rt +9 4.18.0-553.158.1.rt7.499.el8_10 ALSA-2026:59737
AlmaLinux 8 perf +24 4.18.0-553.158.1.el8_10 ALSA-2026:59821

Rocky Linux

Errata ↗
ReleasePackageFixed inAdvisory
Rocky Linux 10 kernel 6.12.0-211.49.1.el10_2 RLSA-2026:57251
Rocky Linux 9 kernel 5.14.0-687.44.1.el9_8 RLSA-2026:63129
Rocky Linux 8 kernel 4.18.0-553.158.1.el8_10 RLSA-2026:59821
Rocky Linux 8 kernel-rt 4.18.0-553.158.1.rt7.499.el8_10 RLSA-2026:59737
ReleasePackageFixed inAdvisory
SLES 15 SP7 kernel-64kb +7 6.4.0-150700.53.81.1 SUSE-SU-2026:4254-1
SLES 15 SP7 kernel-default-base 6.4.0-150700.53.81.1.150700.17.45.1 SUSE-SU-2026:4254-1
SLES 15 SP6 kernel-64kb +6 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLES 15 SP6 kernel-default-base 6.4.0-150600.23.135.1.150600.12.62.4 SUSE-SU-2026:4369-1
Show 9 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
SLES for SAP 16.0 kernel-64kb +8 6.12.0-160000.37.1 SUSE-SU-2026:23231-1, SUSE-SU-2026:23221-1
SLES for SAP 16.0 kernel-default-base 6.12.0-160000.37.1.160000.2.19 SUSE-SU-2026:23231-1, SUSE-SU-2026:23221-1
SLES for SAP 15 SP6 kernel-default-base 6.4.0-150600.23.135.1.150600.12.62.4 SUSE-SU-2026:4369-1
SLES for SAP 15 SP6 kernel-docs +4 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLES 16.0 kernel-64kb +8 6.12.0-160000.37.1 SUSE-SU-2026:23237-1, SUSE-SU-2026:23231-1, SUSE-SU-2026:23221-1
SLES 16.0 kernel-default-base 6.12.0-160000.37.1.160000.2.19 SUSE-SU-2026:23231-1, SUSE-SU-2026:23221-1
SLE Micro 6.2 kernel-default-base 6.12.0-160000.37.1.160000.2.19 SUSE-SU-2026:23068-1
SLE Micro 6.2 kernel-rt +5 6.12.0-160000.37.1 SUSE-SU-2026:23068-1, SUSE-SU-2026:23066-1
SLE Micro 6.1 kernel-default-base 6.4.0-52.1.21.34 SUSE-SU-2026:23529-1
SLE Micro 6.1 kernel-rt +4 6.4.0-52.1 SUSE-SU-2026:23529-1, SUSE-SU-2026:23528-1
SLE Micro 6.0 kernel-default-base 6.4.0-52.1.21.36 SUSE-SU-2026:23481-1
SLE Micro 6.0 kernel-rt +4 6.4.0-52.1 SUSE-SU-2026:23481-1, SUSE-SU-2026:23477-1
SLE Live Patching 15 SP7 kernel-default 6.4.0-150700.53.81.1 SUSE-SU-2026:4254-1
SLE Live Patching 15 SP7 kernel-livepatch-SLE15-SP7-RT_Update_20 1-150700.1.3.1 SUSE-SU-2026:4120-1
SLE Live Patching 15 SP7 kernel-livepatch-SLE15-SP7_Update_21 1-150700.15.3.1 SUSE-SU-2026:4254-1
SLE Live Patching 15 SP6 kernel-default 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLE Live Patching 15 SP6 kernel-livepatch-SLE15-SP6_Update_31 1-150600.13.3.4 SUSE-SU-2026:4369-1
SUSE Real Time Module 15 SP7 kernel-rt +2 6.4.0-150700.7.75.1 SUSE-SU-2026:4120-1
ReleasePackageFixed inAdvisory
openSUSE Leap 16.0 kernel-default-base 6.12.0-160000.37.1.160000.2.19 openSUSE-SU-2026:21555-1
openSUSE Leap 16.0 kernel-rt +11 6.12.0-160000.37.1 openSUSE-SU-2026:21555-1

Amazon Linux

ReleasePackageFixed inAdvisory
Amazon Linux 2023 kernel-livepatch-6.18.35-68.127 +2 1:1.0-0.amzn2023 ALAS2023-2026-1968, ALAS2023-2026-1924, ALAS2023-2026-1881
Amazon Linux 2023 perf +11 1:6.1.176-220.358.amzn2023 ALAS2023-2026-1924
Amazon Linux 2023 perf6.12 +11 1:6.12.94-123.174.amzn2023 ALAS2023-2026-1968
Amazon Linux 2023 perf6.18 +12 1:6.18.35-68.127.amzn2023 ALAS2023-2026-1881

Oracle Linux

ReleasePackageFixed inAdvisory
Oracle Linux 10 rv +29 6.12.0-211.49.1.el10_2 ELSA-2026-57251
Oracle Linux 8 perf +19 4.18.0-553.158.1.el8_10 ELSA-2026-59821

Advisories 50

References