CVE-2021-23718Public exploitNetwork attack vector

Internal data access via unchecked IPv6 addresses

Published Nov 22, 2021 · Updated Sep 16, 2024

SSRF in welefen ssrf-agent before 1.0.5 allows remote attackers to read network-accessible data through crafted IPv6 URLs. The defaultIpChecker function tests private status only for IPv4 values and accepts every non-IPv4 value, allowing private IPv6 destinations. Exploitation requires a consuming application to pass attacker-controlled URLs to the agent; resulting requests can reach IPv6 services inaccessible to the attacker directly.

CVSS severity7.5
High
EPSS probability1.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in welefen ssrf-agent before 1.0.5 allows remote attackers to read network-accessible data through crafted IPv6 URLs. The defaultIpChecker function tests private status only for IPv4 values and accepts every non-IPv4 value, allowing private IPv6 destinations. Exploitation requires a consuming application to pass attacker-controlled URLs to the agent; resulting requests can reach IPv6 services inaccessible to the attacker directly.

The record

CVE
CVE-2021-23718
Published
Nov 22, 2021
Updated
Sep 16, 2024
Vendor
welefen
Product
ssrf-agent
Classifications
CWE-918, CAPEC-664
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <1.0.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

welefen · ssrf-agentversion=unspecified <1.0.5

Published CVSS scores

6.5SnykCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
6.2SnykCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N/E:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
CAPEC-664Server Side Request Forgery

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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