CVE-2026-87864: IMAP APPEND plus CRLF conversion command injection

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-20 · updated 2026-10-30
Weakness: CWE-130

Description

Enabling `CURLOPT_CRLF` causes curl to advertise the raw input byte count in the `IMAP APPEND {N}` literal while transmitting line-ending expanded data. The server reads only $N$ bytes for the payload, causing the remaining overflow bytes to be interpreted and executed as pipelined IMAP commands within the authenticated session.

Affected products

curl: from 8.21.0 through 8.21.0; from 8.20.0 through 8.20.0; from 8.19.0 through 8.19.0; from 8.18.0 through 8.18.0; from 8.17.0 through 8.17.0; from 8.16.0 through 8.16.0

References

https://curl.se/docs/CVE-2026-87864.html
https://curl.se/docs/CVE-2026-87864.json
https://hackerone.com/reports/3972403
https://hackerone.com/reports/3972403

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