CVE-2023-27533Public exploitNetwork attack vector

TELNET command injection via unsanitized negotiation fields

Published Mar 30, 2023 · Updated Feb 13, 2026

Protocol injection in curl 7.7 through 7.88.1 allows attackers to alter TELNET negotiation through crafted usernames or options. The check_telnet_options function in lib/telnet.c passed non-ASCII bytes from usernames and option arguments into the protocol stream, permitting embedded IAC commands. Reachability requires an application to accept attacker-controlled parts of those fields; the result is unintended content or option negotiation with the TELNET server.

CVSS severity8.8
High
EPSS probability1.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Protocol injection in curl 7.7 through 7.88.1 allows attackers to alter TELNET negotiation through crafted usernames or options. The check_telnet_options function in lib/telnet.c passed non-ASCII bytes from usernames and option arguments into the protocol stream, permitting embedded IAC commands. Reachability requires an application to accept attacker-controlled parts of those fields; the result is unintended content or option negotiation with the TELNET server.

The record

CVE
CVE-2023-27533
Published
Mar 30, 2023
Updated
Feb 13, 2026
Vendor
curl
Product
curl
Classifications
CWE-75, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 30, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2026Record 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=Fixed in 8.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=Fixed in 8.0.0

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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-75Failure to Sanitize Special Elements into a Different Plane
T1203Exploitation for Client Execution

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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