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PatchSiren cyber security CVE debrief

CVE-2026-47734 jelmer CVE debrief

CVE-2026-47734 is a MEDIUM-severity vulnerability in Dulwich, a pure-Python implementation of Git file formats and protocols. The issue allows a client with push access to cause a denial of service by pushing a crafted thin pack that declares a huge dest_size, leading to excessive memory allocation. This vulnerability affects operators running a Dulwich-based Git server that exposes git-receive-pack. The issue is patched in Dulwich version 1.2.5.

Vendor
jelmer
Product
dulwich
CVSS
MEDIUM 5.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-10
Original CVE updated
2026-06-11
Advisory published
2026-06-10
Advisory updated
2026-06-11

Who should care

Operators running a Dulwich-based Git server that exposes git-receive-pack, particularly those who accept pushes from untrusted clients.

Technical summary

A client with push access can push a tiny crafted thin pack (~174 bytes) with a delta header declaring a huge dest_size. When Dulwich ingests it via add_thin_pack / apply_delta, it allocates hundreds of MB of memory based on the attacker-controlled size, with no relation to the actual bytes received.

Defensive priority

High

Recommended defensive actions

  • Upgrade to Dulwich 1.2.5 or later.
  • Set receive.maxInputSize in the server's repository config to a sane bound for the environment.
  • Restrict dulwich-receive-pack (push) access to trusted, authenticated clients only.
  • Disable dulwich-receive-pack 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).

Evidence notes

The vulnerability is patched in Dulwich version 1.2.5. Users should upgrade and set receive.maxInputSize in their server's repository config.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-47734 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-47734

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-47734 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-47734

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.