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

Description

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.1.0 and prior to version 1.2.5, 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. 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 - are impacted. The issue is 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. 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 and/or 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.

Scores

EPSS (exploitation in 30 days)

0.19% · top 92% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.7.

Weakness

• CWE-400: Uncontrolled Resource Consumption (opens in a new tab)All about CWE-400 and its CVEs
• CWE-789: Memory Allocation with Excessive Size Value (opens in a new tab)All about CWE-789 and its CVEs

Affected products

• jelmer · dulwich

  • affected >= 0.1.0, < 1.2.5

Affected packages

From reviewed advisories of the GitHub Advisory Database.

• PyPIdulwichGHSA-xrvj-v92f-53gj (opens in a new tab)

References (2)

• https://github.com/jelmer/dulwich/security/advisories/GHSA-xrvj-v92f-53gj (opens in a new tab)x_refsource_CONFIRM
• https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5 (opens in a new tab)x_refsource_MISC

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisory GHSA-xrvj-v92f-53gj (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-47734](https://trackcve.app/badge/CVE-2026-47734.svg)](https://trackcve.app/cve/CVE-2026-47734)

Record last updated 11 Jun 2026, 16:14 UTC.