{"id":"PYSEC-2026-2466","summary":"Dulwich has unbounded memory allocation in receive-pack from crafted thin packs","details":"## Impact\n\nAn uncontrolled-resource-consumption (memory exhaustion) denial-of-service vulnerability (CWE-400 / CWE-789).\n\nA 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.\n\nWho is impacted: Operators running a Dulwich-based Git server that exposes git-receive-pack (i.e. accepts pushes) -\nfor example via dulwich.server functionality, the HTTP  smart server, or anything built on ReceivePackHandler. \n\n## Patches\n\nPatched in 1.2.5.\n\nadd_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.\n\nUsers 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.\n\n## Workarounds\n\nOn unpatched versions, receive.maxInputSize has no effect, so it cannot be used as a workaround. Until upgrading, operators should:\n\n- Restrict dulwich-receive-pack (push) access to trusted, authenticated clients only, or disable it entirely on servers that only need to serve fetches.\n- 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.\n\n##  Resources\n\n- git's receive.maxInputSize / git index-pack --max-input-size documentation \n- Reported by Liyi, Ziyue, Strick, Maurice and Chenchen @ University of Sydney","aliases":["CVE-2026-47734","GHSA-xrvj-v92f-53gj"],"modified":"2026-07-13T16:31:41.594863437Z","published":"2026-07-13T15:46:15.665113Z","references":[{"type":"WEB","url":"https://github.com/jelmer/dulwich/security/advisories/GHSA-xrvj-v92f-53gj"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47734"},{"type":"PACKAGE","url":"https://github.com/jelmer/dulwich"},{"type":"WEB","url":"https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5"},{"type":"PACKAGE","url":"https://pypi.org/project/dulwich"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-xrvj-v92f-53gj"}],"affected":[{"package":{"name":"dulwich","ecosystem":"PyPI","purl":"pkg:pypi/dulwich"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.1.0"},{"fixed":"1.2.5"}]}],"versions":["0.1.0","0.1.1","0.10.0","0.10.1a","0.11.0","0.11.1","0.11.2","0.12.0","0.13.0","0.14.0","0.14.1","0.15.0","0.16.0","0.16.1","0.16.2","0.16.3","0.17.1","0.17.2","0.17.3","0.18.0","0.18.1","0.18.2","0.18.3","0.18.4","0.18.5","0.18.6","0.19.0","0.19.1","0.19.10","0.19.11","0.19.12","0.19.13","0.19.14","0.19.15","0.19.16","0.19.2","0.19.3","0.19.3a0","0.19.4","0.19.5","0.19.6","0.19.7","0.19.8","0.19.9","0.2.1","0.20.0","0.20.1","0.20.10","0.20.11","0.20.12","0.20.13","0.20.14","0.20.15","0.20.17","0.20.18","0.20.19","0.20.2","0.20.20","0.20.21","0.20.22","0.20.23","0.20.24","0.20.25","0.20.26","0.20.27","0.20.28","0.20.29","0.20.3","0.20.30","0.20.31","0.20.32","0.20.33","0.20.34","0.20.35","0.20.36","0.20.37","0.20.38","0.20.39","0.20.4","0.20.40","0.20.41","0.20.42","0.20.43","0.20.44","0.20.45","0.20.46","0.20.47","0.20.48","0.20.49","0.20.5","0.20.50","0.20.6","0.20.7","0.20.8","0.20.9","0.21.0","0.21.1","0.21.2","0.21.3","0.21.4","0.21.4.1","0.21.5","0.21.6","0.21.7","0.22.0","0.22.1","0.22.3","0.22.4","0.22.5","0.22.6","0.22.7","0.22.8","0.23.0","0.23.1","0.23.2","0.24.0","0.24.1","0.24.10","0.24.2","0.24.3","0.24.4","0.24.5","0.24.6","0.24.7","0.24.8","0.24.9","0.25.0","0.25.1","0.25.2","0.3.0","0.3.1","0.3.2","0.3.3","0.4.0","0.4.1","0.5.0","0.6.0","0.6.1","0.6.2","0.7.0","0.7.1","0.8.0","0.8.1","0.8.2","0.8.3","0.8.4","0.8.5","0.8.6","0.8.7","0.9.0","0.9.1","0.9.2","0.9.3","0.9.4","0.9.5","0.9.6","0.9.7","0.9.8","0.9.9","1.0.0","1.1.0","1.2.0","1.2.1","1.2.2","1.2.3","1.2.4"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/dulwich/PYSEC-2026-2466.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H"}]}