{"affected":[{"ranges":[{"events":[{"introduced":"d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c"},{"fixed":"8a14632ca6ba8a8afd2a3f2098bc267c13e13d93"},{"fixed":"69489f8b74213f03db10169e6e5407e6d5fee512"}],"repo":"https://github.com/hexpm/hex","type":"GIT"}]}],"aliases":["GHSA-98jr-23pm-vj7c","CVE-2026-105280"],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Eric Meadows-Jönsson","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}],"database_specific":{"capec_ids":["CAPEC-186"],"cpe_ids":["cpe:2.3:a:hexpm:hex:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-354"]},"details":"## Summary\n\nImproper Validation of Integrity Check Value vulnerability in hexpm hex allows a package mirror to substitute the tarball that `mix hex.package fetch PACKAGE VERSION --output -` writes to standard output.\n\nHex compares a fetched tarball's inner and outer checksums with the repository's signed registry before writing it to a file or unpacking it. The standard output branch of `mix hex.package fetch` writes the bytes returned by `Hex.SCM.fetch/3` without that comparison, and `Hex.SCM.fetch/3` doesn't verify freshly downloaded tarballs itself. When a mirror configured with `HEX_MIRROR_URL` or `mirror_url` serves altered bytes, the command prints them and exits successfully, while the same fetch with `--output FILE` fails with a checksum mismatch.\n\nHex also prints diagnostics to standard output while the command runs: the body of a failed HTTP response from the update check or a registry fetch, and API warnings from the `x-hex-message` header. A mirror that answers one of those requests with an error whose body is a tar archive gets that archive written to standard output ahead of the verified tarball, so a pipeline that unpacks standard output extracts the mirror's files. This happens even when the checksum check then fails, because the archive is already on standard output.\n\nThis issue affects hex: from 0.20.2 before 2.5.2.\n\n## Details\n\n1. `mix hex.package fetch PACKAGE VERSION --output -` calls `fetch_tarball!/3`, which calls `Hex.SCM.fetch/3`.\n2. For a fresh download, `Hex.SCM.fetch/3` writes the response body to the cache and returns it without comparing it to the registry checksum.\n3. The standard output branch passes those bytes to `IO.binwrite/1`. The file and `--unpack` branches call `verify_inner_checksum!/4` and `verify_outer_checksum!/4` first.\n4. While the task runs, Hex prints messages with `Hex.Shell.info/1`, which writes to standard output. `Hex.Utils.print_error_result/1` prints the body of an error response that way; the update checker calls it when its request for `installs/hex-1.x.csv` fails, and `Hex.Registry.Server` calls it when a registry fetch fails and the cached registry is used. `Hex.HTTP` prints the `x-hex-message` warning of each response the same way. These are printed before the tarball is written, so the mirror chooses bytes that come before the tarball on standard output.\n\n## Proof of concept\n\n1. Set `HEX_MIRROR_URL` to a server that returns modified bytes for `tarballs/decimal-2.4.1.tar` and proxies everything else to repo.hex.pm.\n2. `mix hex.package fetch decimal 2.4.1 --output -` prints the modified bytes and exits 0.\n3. `mix hex.package fetch decimal 2.4.1 --output decimal.tar` fails with `Checksum mismatch against registry (outer)`.\n\n## Impact\n\nHex treats mirrors as untrusted and relies on registry signatures and checksums for package integrity. Scripts that pipe `mix hex.package fetch --output -` into another tool, such as an unpacker, a vendoring step or an installer, receive whatever the mirror served, so the mirror operator can deliver modified package contents that downstream steps treat as the published release.\n\n## Workarounds\n\nWrite the tarball to a file with `--output FILE`, which verifies the checksums, and read that file instead of standard output.\n\n## Configurations\n\nAffects `mix hex.package fetch` with `--output -` when packages are downloaded through a mirror set with `HEX_MIRROR_URL` or `mirror_url`. Downloads directly from the repository over HTTPS aren't affected unless TLS verification is broken.\n\n## Solutions\n\nUpgrade Hex to 2.5.2 or later, for example with `mix local.hex`. `mix hex.package fetch PACKAGE VERSION --output -` then verifies the registry checksum before writing the tarball to standard output and prints its messages to standard error.","id":"EEF-CVE-2026-105280","modified":"2026-10-12T15:30:14.633634Z","published":"2026-10-12T15:30:14.126Z","references":[{"type":"ADVISORY","url":"https://github.com/hexpm/hex/security/advisories/GHSA-98jr-23pm-vj7c"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-105280.html"},{"type":"WEB","url":"https://github.com/hexpm/hex/commit/d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c"},{"type":"FIX","url":"https://github.com/hexpm/hex/commit/8a14632ca6ba8a8afd2a3f2098bc267c13e13d93"},{"type":"FIX","url":"https://github.com/hexpm/hex/commit/69489f8b74213f03db10169e6e5407e6d5fee512"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","type":"CVSS_V4"}],"summary":"Hex writes unverified package tarballs to standard output in mix hex.package fetch","upstream":[]}