Reproducible Builds in July 2026

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Welcome to the July 2026 report from the Reproducible Builds project!

In our reports, we try to outline the most important things that we have been up to over the past month. As a quick recap about what problem our project intends to solve, whilst anyone may inspect the source code of free software for malicious flaws, almost all software is distributed to end users as pre-compiled binaries. The motivation behind the reproducible builds effort is to ensure no flaws have been introduced during this compilation process by promising identical results are always generated from a given source, thus allowing multiple third-parties to come to a consensus on whether a build was compromised or not.

If you are interested in contributing to the project, please visit the Contribute page on our website.

In this month’s report, we cover:

  1. Tool development
  2. Distribution work
  3. Three new scholarly papers
  4. Patches
  5. Misc news

Tool development

diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb made the following changes, including preparing and uploading versions 324, 325 and 326 to Debian:

  • Fix tests to work with zipdetails 4.0008. (#1141359)
  • Bump debhelper compatibility level to 13. […]
  • Update copyright years. […]

In addition, Paul Spooren made changes to allow trailing garbage in Gzip files […] and Vagrant Cascadian added an external tool reference for the pedump binary to use the mono package under GNU Guix. […]


disorderfs is our FUSE-based filesystem that deliberately introduces non-determinism into system calls to reliably flush out reproducibility issues. This month, Christelle Gloor added the option to sort by ctime as returned by the lstat(2) syscall. […], which Chris Lamb uploaded whilst bumping the Standards-Version to version 4.7.4 […]. Bernhard Wiedemann also updated disorderfs to version 0.7.0 in openSUSE.


Yet again, there were a number of improvements made to our website this month as well. For example, Chris Lamb, by request of Digital Ocean, changed the target of a referral link so that they can manage incoming referrers […] and pushed a number of changes to the Tools page […].


Distribution work

In Debian this month, 32 reviews of Debian packages were added, 26 were updated and a total of 21 were removed this month, adding to our extensive knowledge about identified issues.

A number of issue types were added by Chris Lamb, including:

  • python_towncrier_build_date […][…]
  • log_files_installed_in_package […]
  • fontforge_varies_by_timezone […][…]

Chris also added a further note for the build_date_in_manpage_generated_by_spf13_cobra issue. […]


In addition, there is a new page showing verification rebuilds of OpenWrt APK packages and firmware images, powered by rebuilderd:


Three new scholarly papers

Yan Li, Nan Jiang, Qihang Zhou, Shaowen Xu, Yamin Xie and Xiaoqi Jia of the Chinese Academy of Sciences published a paper titled VCAligner: Aligning Source Distribution Versions with Upstream Git Commits to Secure Supply Chain:

We present VCAligner, a content-based alignment methodology that constructs inverted indexes over VCS histories to precisely map released artifacts to their originating commits, independent of fragile version tags. We evaluated VCAligner on a dataset of 2,984 verifiable PyPI packages derived from the 4,000 most-downloaded projects linked to public GitHub upstreams. Our results reveal a critical weakness in conventional tag-based heuristics: while they appear effective on 85% of the dataset, the residual 15% failure rate generates a catastrophic downstream audit workload of over 10.3 million commits. In contrast, VCAligner reduces this burden by two orders of magnitude (≈ 158×), bounding the total workload to under 65,000 commits. Furthermore, we provide the large-scale characterization of “Packaging Noise,” classifying artifact divergence into structural additions (Path Phantoms) and content mutations (Blob Phantoms), thereby isolating the distinct attack surfaces of malicious injection and code tampering.


Jens Dietrich and Spencer Sun from the Victoria University of Wellington together with Tim W. White and Behnaz Hassanshahi from Oracle Inc pre-published their paper No Snake Oil: Verifying Python Package Builds (PDF):

Python has become the default language for interacting with AI, with packages being distributed through registries like the Python Package Index (PyPI). This creates a need to analyse supply chains comprising such packages. One such analysis is to rebuild packages in order to identify compromised builds injecting malware. Independent rebuilds in hardened environments have the added advantage that they can generate and record provenance in order to increase the trustworthiness of packages. Two tools that are designed to automate such rebuilds and run them at scale are macaron and oss-rebuild. We study 12,180 popular releases from PyPI and find that the byte-for-byte equivalence rate is generally low. We analyse the reasons why they produce different wheels, and find that equivalence between the original and rebuilt wheels can often still be established, preserving most of the guarantees users expect from rebuildable releases. We present and evaluate daleq4py, a tool to establish the equivalence of Python wheels through the kernel of a normalisation function that is based on provenance-preserving datalog rules. Experimental results show that daleq4py substantially expands the set of rebuilds that can be accepted as equivalent. Although only 15.4% of macaron rebuilds and 19.1% of oss-rebuild rebuilds are byte-for-byte identical to the published PyPI wheels, daleq4py establishes wheel equivalence for 60.2% and 78.9% of source-equivalent rebuilds, respectively.


Denise Nanni, Julien Malka, Stefano Zacchiroli and Théo Zimmermann from Télécom Paris together with Gabriele D’Angelo from the University of Bologna pre-published their paper Understanding Build Reproducibility in the F-Droid Ecosystem (PDF), which was accepted at the 2026 ACM Conference on Reproducibility and Replicability:

The security of open source applications benefits considerably from the possibility of rebuilding their source and verifying the output. F-Droid, a prominent distribution for open source Android applications, systematically rebuilds them from source and tests their bitwise reproducibility at app publishing time. However, F-Droid offers no guarantee that app reproducibility will continue to hold in the future. As software ecosystems evolve, reproducibility may degrade, with potential negative consequences for software preservation and security. We present the first empirical study of build reproducibility in the F-Droid app ecosystem. Analyzing historical reproducibility logs, we find that the overall bitwise reproducibility rate has been steadily increasing over time (as new versions of apps are published). We then evaluate how reproducibility holds in time for fixed app versions, by attempting to rebuild 18 904 app versions that F-Droid had previously confirmed bitwise reproducible, published between September 2018 and February 2026, achieving an 83% rebuild success rate, and identify missing dependencies as the dominant cause of failure, accounting for 76% of non-rebuildable cases. Among successfully rebuilt apps, 94% are also bitwise reproducible-i.e., they still yield bitwise identical artifacts upon rebuild. Together, these results show that while bitwise reproducibility largely holds for apps that can be rebuilt, rebuildability itself is highly sensitive to temporal decay.


Patches

The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where applicable or possible. This month, we wrote a large number of such patches, including:


Misc news

On our mailing list this month, Colin Winter of Markovian Protocol wrote to our mailing list on the topic of Reproducible verification for retained logs:

Reproducible builds remove trust in the builder: anyone re-derives the same artifact from the same source, byte for byte. The same shape applies one layer over, to a retained record. Most record-keeping regimes (the EU AI Act’s Article 12 logging is the current example) require that events be recorded and logs retained, but not that a retained log be verifiable, by a party who was not present, as unaltered and existing when claimed. That leaves an integrity obligation resting on trusting the party being audited.

(Full thread)



Finally, if you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:



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