ALAS2023-2026-2026

References: CVE-2026-38974  CVE-2026-42305  CVE-2026-47734 
FAQs regarding Amazon Linux ALAS/CVE Severity

Issue Overview:

Dulwich through 1.1.0 was found to be missing SSH host key verification in contrib/paramiko_vendor.py. (CVE-2026-38974)

Arbitrary file write leading to remote code execution when cloning or checking out a malicious Git repository on Windows.

Dulwich's path-element validator accepted tree entries whose filenames contained bytes that Windows interprets as structural path syntax:

\ -- the Windows path separator. A single tree entry named .git\hooks\pre-commit.exe was treated as one valid filename on POSIX but materialized as nested directories .git/hooks/pre-commit.exe on Windows, planting a file inside the victim's .git directory. Git for Windows then
executes that hook on the next git commit, giving the attacker arbitrary code execution in the victim's user context. The same primitive can be used with ..\outside.txt to escape the work tree.
: -- the NTFS alternate-data-stream marker. .git::$INDEX_ALLOCATION writes directly into the victim's .git entity, bypassing the .git-as-a-directory check.
git~ -- NTFS 8.3 short-name aliases of .git. Only the literal git1 was rejected; git2, git10, GIT1, etc. were all accepted.
Contributing configuration bugs made matters worse. The core.protectNTFS and core.protectHFS settings were looked up under a wrong option name and so user-set values were silently ignored, and core.protectNTFS only defaulted to true on Windows (Git upstream has defaulted it to true everywhere since CVE-2019-1353). Both have been corrected.

Anyone who clones, fetches, or checks out an untrusted repository with Dulwich on Windows - either through the Dulwich CLI, porcelain.clone, or any downstream tool built on Dulwich - is impacted. POSIX clones are not directly exploitable (on POSIX \ is a literal filename byte), but a POSIX user can unknowingly propagate a malicious tree to Windows consumers via push or re-publication. (CVE-2026-42305)

An uncontrolled-resource-consumption (memory exhaustion) denial-of-service vulnerability (CWE-400 / CWE-789).

A client with push access could push a tiny crafted thin pack (~174 bytes) whose delta header declares a huge dest_size. When dulwich ingested it via add_thin_pack / apply_delta, it would allocate hundreds of MB of memory based on that attacker-controlled size, with no relationship to the actual bytes received.

Who is impacted: Operators running a dulwich-based Git server that exposes git-receive-pack (i.e. accepts pushes) -
for example via dulwich.server functionality, the HTTP smart server, or anything built on ReceivePackHandler. (CVE-2026-47734)

Issue Correction:
Run dnf update python-dulwich --releasever 2023.12.20260803 or dnf update --advisory ALAS2023-2026-2026 --releasever 2023.12.20260803 to update your system.
More information on how to update your system can be found on this page: Amazon Linux 2023 documentation

New Packages:

aarch64:
    python-dulwich-debugsource-0.20.18-1.amzn2023.0.3.aarch64
    python-dulwich-doc-0.20.18-1.amzn2023.0.3.aarch64
    python3-dulwich-debuginfo-0.20.18-1.amzn2023.0.3.aarch64
    python3-dulwich-0.20.18-1.amzn2023.0.3.aarch64

src:
    python-dulwich-0.20.18-1.amzn2023.0.3.src

x86_64:
    python-dulwich-debugsource-0.20.18-1.amzn2023.0.3.x86_64
    python3-dulwich-debuginfo-0.20.18-1.amzn2023.0.3.x86_64
    python-dulwich-doc-0.20.18-1.amzn2023.0.3.x86_64
    python3-dulwich-0.20.18-1.amzn2023.0.3.x86_64