Dulwich has unbounded memory allocation in receive-pack from crafted thin packs
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
Betroffene Software
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| Plattform | Paket | Anfällige Versionen | Behoben in |
|---|---|---|---|
| Python (PyPI) | dulwich | >= 0.1.0, < 1.2.5 | 1.2.5 |
Verweise
- CVSS-Vektor
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H- Schwäche (CWE)
CWE-400, CWE-789- Plattform
- Python (PyPI)
- Paket
dulwich- Veröffentlicht
- 08.06.2026
- Aktualisiert
- 11.10.2026 14:18
Quellen und Lizenzen
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
Schwachstellenhistorie: dulwich
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- Einträge insgesamt
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- 03.2015 10.2026
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