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Medium

Dulwich has unbounded memory allocation in receive-pack from crafted thin packs

  • Disclosed: 08.06.2026
  • Updated: 11.10.2026 14:18

Impact

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.

Patches

Patched in 1.2.5.

add_thin_pack now accepts a max_input_size keyword (bytes; 0/None = unlimited, matching git's semantics), and ReceivePackHandler reads receive.maxInputSize from the repository config and passes it through. Wire reads are counted and a PackInputTooLarge exception is raised once the cap is exceeded - equivalent to git index-pack --max-input-size.

Users should upgrade to Dulwich 1.2.5 or later and set receive.maxInputSize in their server's repository config to a sane bound for their environment.

Workarounds

On unpatched versions, receive.maxInputSize has no effect, so it cannot be used as a workaround. Until upgrading, operators should:

  • Restrict dulwich-receive-pack (push) access to trusted, authenticated clients only, or disable it entirely on servers that only need to serve fetches.
  • Run the server under an OS-level memory limit (e.g. ulimit, cgroups/MemoryMax, or a container memory limit) so a malicious push is killed rather than taking down the host.

Resources

  • git's receive.maxInputSize / git index-pack --max-input-size documentation
  • Reported by Liyi, Ziyue, Strick, Maurice and Chenchen @ University of Sydney

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) dulwich >= 0.1.0, < 1.2.5 1.2.5

References

CVSS score 5.7/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-400, CWE-789
Platform
Python (PyPI)
Package
dulwich
Disclosed
08.06.2026
Updated
11.10.2026 14:18

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-2466 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-xrvj-v92f-53gj - CC BY 4.0

Vulnerability history: dulwich

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (13) in the archive
Total entries
13
First → latest
03.2015 10.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 3
  • High 7
  • Medium 2
  • Low 1

Disclosures per year

earlier: 2

Severity:
  1. Dulwich: Arbitrary File Write (RCE) on Windows via Unvalidated Drive Letters in Tree Paths
    High · 8.8 ghsa-8mcx-5rqc-vhmf < 1.2.9 1.2.9
  2. Dulwich: Symlink write-through in checkout(paths=[]) via raw os.open bypasses all symlink protections
    High · 8.6 ghsa-8w8g-wq8h-fq33 >= 0.24.0, < 1.2.8 1.2.8
  3. Dulwich: Symlink directory traversal in filter-branch index_filter via cross-commit state persistence
    High · 8.6 ghsa-5fqc-mrg8-w798 >= 0.23.1, < 1.2.8 1.2.8
  4. Dulwich: Symlink directory traversal in stash pop allows arbitrary file write via intermediate directory symlinks
    High · 8.6 ghsa-cm62-gvxx-vmxx >= 0.22.5, < 1.2.8 1.2.8
  5. Dulwich's submodule path traversal in porcelain.submodule_update / porcelain.clone(recurse_submodules=True) yields RCE via attacker-dropped .git/hooks payload
    High · 7.5 CVE-2026-52726 >= 0.23.2, < 1.2.5 1.2.5
  6. Dulwich has unbounded memory allocation in receive-pack from crafted thin packs this entry
    Medium · 5.7 CVE-2026-47734 >= 0.1.0, < 1.2.5 1.2.5
  7. Dulwich Vulnerable to Command Injection via Merge Driver Path
    High CVE-2026-42563 >= 0.24.0, < 1.2.5 1.2.5
  8. Dulwich has an arbitrary file write via NTFS-hostile tree entries on Windows
    High · 8.8 CVE-2026-42305 >= 0.10.0, < 1.2.5 1.2.5
  9. Dulwich before 0.18.5, when an SSH subprocess is used, allows remote attackers to execute arbitrary commands via an ssh URL with an initial dash character in the hostname, a related issue to CVE-2017-
    Critical · 9.8 CVE-2017-16228 < 0.18.5 0.18.5
  10. The build_index_from_tree function in index.py in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a commit with a directory path starting with .git/, which is not properly h
    Critical · 9.8 CVE-2014-9706 < 0.9.9 0.9.9
  11. Buffer overflow in the C implementation of the apply_delta function in _pack.c in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a crafted pack file.
    Critical · 9.8 CVE-2015-0838 < 0.9.9 0.9.9

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