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Vulnerability Database

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A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

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363,159

Total vulnerabilities in the database

CVE-2026-55495 — github.com/cloudreve/Cloudreve/v4

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Summary

Cloudreve's WOPI PUT_RELATIVE handler treats X-WOPI-SuggestedTarget as a path, not a filename. It splits the header on / and joins the segments onto the source file's directory with URI.JoinRaw, which feeds Go's url.JoinPath. url.JoinPath resolves ./.. segments, so a slash-bearing target such as a/../../evil.docx collapses to a location outside the source file's directory. The lower-level upload path then validates only the final, already-cleaned basename (evil.docx), which is harmless, and checks ownership against the resolved ancestor — which is still the same user's drive.

A WOPI access token is bound to exactly one file (the route enforces fileId == session.FileID with a 403 otherwise). PUT_RELATIVE escapes that per-file scope: a token issued for one file can create (and, conditionally, overwrite) files elsewhere in the same account.

Root cause (verified at `26b6b10`)

1. Token is single-file scoped (the boundary being escaped) — middleware ViewerSessionValidation:

fileId := hashid.FromContext(c)
if fileId != session.FileID {           // 403 — token is bound to ONE file
    c.Status(http.StatusForbidden); c.Abort(); return
}

Route: wopi := noAuth.Group("file/wopi", middleware.HashID(hashid.FileID), middleware.ViewerSessionValidation()); wopi.POST(":id", controllers.ModifyFile) → POST /api/v4/file/wopi/:id?access_token=<token>.

2. PUT_RELATIVE dispatch — routers/controllers/wopi.go:

case wopi.MethodPutRelative:            // X-WOPI-Override: PUT_RELATIVE
    err = service.PutContent(c, true)

3. SuggestedTarget joined as a path — service/explorer/viewer.go:

fileName, _ := wopi.UTF7Decode(c.GetHeader(wopi.SuggestedTargetHeader)) // X-WOPI-SuggestedTarget
fileUriParsed, _ := fs.NewUriFromString(fileUri)
if strings.HasPrefix(fileName, &quot;.&quot;) { /* treat as extension */ }
fileUri = fileUriParsed.DirUri().JoinRaw(fileName).String()             // &lt;-- path join, not basename
...
subService := FileUpdateService{ Uri: fileUri }
res, err := subService.PutContent(c, lockSession)

4. JoinRaw splits on / and normalizes via url.JoinPath — pkg/filemanager/fs/uri.go:

func (u *URI) Join(elem ...string) *URI {
    newUrl, _ := url.Parse(u.U.String())
    return &amp;URI{U: newUrl.JoinPath(/* PathEscape each elem */ ...)} // JoinPath cleans ./ and ../
}
func (u *URI) JoinRaw(elem string) *URI {
    return u.Join(strings.Split(strings.TrimPrefix(elem, Separator), Separator)...)
}

PathEscape leaves . unescaped (it is in the unreserved set), so .. segments survive into JoinPath, which resolves them. URI.Name() returns path.Base(path.Clean(path)) — the cleaned basename.

5. Upload checks ownership of the resolved ancestor and validates only the clean basename — pkg/filemanager/fs/dbfs/upload.go:

ancestor, err := f.getFileByPath(ctx, navigator, req.Props.Uri)        // URI already traversal-normalized
...
if _, ok := ctx.Value(ByPassOwnerCheckCtxKey{}).(bool); !ok &amp;&amp; ancestor.OwnerID() != f.user.ID {
    return nil, fs.ErrOwnerOnly                                        // same-user -&gt; passes
}
...
if err := validateNewFile(req.Props.Uri.Name(), req.Props.Size, policy); err != nil { // checks &quot;evil.docx&quot; only
    return nil, err
}

validateFileName rejects / \ : * ? " < > | and bare ./.. — but the traversal is already gone by the time it sees the basename.

Validation performed

Independent validation against commit 26b6b10 in a clean sandbox.

Source-verified (static): the full chain confirmed verbatim — single-file-scoped token (403 on mismatch) → PUT_RELATIVE dispatch → DirUri().JoinRaw(SuggestedTarget) → url.JoinPath normalization → ancestor ownership check (same-user passes) → basename-only validation of the cleaned name.

Dynamic (control-flow executed): the full binary is not buildable offline here (modules behind an unreachable Go proxy, embedded frontend, DB). I built and ran a harness using the real Go net/url stdlib plus the verbatim Join/JoinRaw/DirUri/Path/Name/PathEscape/shouldEscape and the validateFileName gate, driving the same transformation PUT_RELATIVE performs. Source = cloudreve://my/folder/current.docx:

SuggestedTarget            resolved URI                          final basename   validator
&quot;copy.docx&quot;                cloudreve://my/folder/copy.docx       &quot;copy.docx&quot;      ACCEPT
&quot;a/../../evil.docx&quot;        cloudreve://my/evil.docx              &quot;evil.docx&quot;      ACCEPT   &lt;- ESCAPED to /
&quot;a/../../../top.docx&quot;      cloudreve://my/top.docx               &quot;top.docx&quot;       ACCEPT   &lt;- ESCAPED to /
&quot;sub/evil.docx&quot;            cloudreve://my/folder/sub/evil.docx   &quot;evil.docx&quot;      ACCEPT   &lt;- different subdir
&quot;.pdf&quot;                     cloudreve://my/folder/current.pdf     &quot;current.pdf&quot;    ACCEPT
&quot;a%2f..%2f..%2fenc.docx&quot;   cloudreve://my/folder/a%252f..%252f.. &quot;a%2f..%2f..%2f&quot; ACCEPT   (NO escape)

The headline payload a/../../evil.docx deterministically resolves to cloudreve://my/evil.docx (account root) with a clean, accepted basename. Output matches the original audit probe exactly. Honest caveat: a leading non-.. segment (e.g. a/) is required to prime the join; a single ../evil.docx does not cleanly escape, and URL-encoded separators (%2f) do not traverse through this path (they are re-escaped into one literal segment). Only literal / separators work.

Confidence tier: source-verified + control-flow dynamically reproduced (no full live HTTP write against a deployed instance).

Deduplication: no existing CVE/GHSA matches. Known Cloudreve advisories are CVE-2022-32167 (XSS, v1–v3.5.3) and CVE-2026-25726 (weak-PRNG ATO, instances initialized < v4.10.0) — both unrelated. SECURITY.md lists "user permissions" as high-impact and in scope for all 4.x, so this qualifies as a vulnerability under the project's own policy.

Steps to reproduce

Setup: user owns cloudreve://my/folder/current.docx; open it in the WOPI editor to obtain <token> (the session is bound to that file's ID).

Send the crafted PUT_RELATIVE: POST /api/v4/file/wopi/<file-id>?access_token=<token> HTTP/1.1 Host: target X-WOPI-Override: PUT_RELATIVE X-WOPI-SuggestedTarget: <UTF-7 of "a/../../evil.docx"> Content-Type: application/octet-stream <file bytes>
Cloudreve rewrites the target from cloudreve://my/folder/current.docx to cloudreve://my/evil.docx, validates the basename evil.docx (passes), and writes the content. Expected: the target is rejected or constrained to the source file's directory. Actual: a file is written at the account root, outside the token's single-file scope.

Impact

A WOPI access token scoped to one file can write files to other locations in the same user's account. A malicious or compromised WOPI integration (or a leaked token) can plant or, conditionally, overwrite files at attacker-chosen paths the account owns, defeating the per-file scoping the WOPI session is meant to enforce. Confined to the session user's account (not cross-user).

Remediation

Treat X-WOPI-SuggestedTarget (and X-WOPI-RequestedName) as a filename, not a path: reject /, \, dot segments, and percent-encoded separator variants before joining.
Prefer DirUri().Join(sanitizedBaseName) over JoinRaw, and after constructing the target URI assert it is a direct child of the source file's directory.
Add regression tests for a/../../evil.docx, sub/evil.docx, and encoded-separator variants.

Published: Jul 24, 2026
Updated: Jul 25, 2026
CVE: CVE-2026-55495
GHSA: GHSA-49h3-cwhj-4737
Severity: Medium
Exploit:
CISA KEV:

CVSS v3:

Severity: Low
Score: 4.3
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CWEs:

CWE-22

OWASP TOP 10:

A5 - Broken Access Control

Affected Software
References

Software	From	Fixed in
github.com/cloudreve/Cloudreve/v4	-	4.0.0-20260613023150-7968e50429ef
github.com/cloudreve/Cloudreve/v3	-	3.0.0-20250225100611-da4e44b77af4.x

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.