by Kastro
Paper/Archive/CVE-2026-87866

CVE-2026-87866

curl curl — wolfSSL public-key pinning bypass

EPSS 0.2%public exploitCVSS 9.1
critical.is priorityof 100
40
CVSS 9.1 (ADP)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 10.9.109 × 202.2Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

When built with wolfSSL, curl can successfully validate a pinned public key hash against a key the TLS peer does not possess. During the TLS handshake, wolfSSL validates the connection, but curl's subsequent re-parsing of the same certificate - tricked by a manipulated validity length field - extracts and matches a different embedded key, incorrectly authorizing the pinned public key.

Affected

ProductAffectedFixed inSource
curl8.22.0 – 8.22.0–CNA
curl8.21.0 – 8.21.0–CNA
curl8.20.0 – 8.20.0–CNA
curl8.19.0 – 8.19.0–CNA
curl8.18.0 – 8.18.0–CNA
curl8.17.0 – 8.17.0–CNA
curl8.16.0 – 8.16.0–CNA
curl8.15.0 – 8.15.0–CNA
curl8.14.1 – 8.14.1–CNA
curl8.14.0 – 8.14.0–CNA
curl8.13.0 – 8.13.0–CNA
curl8.12.1 – 8.12.1–CNA

Scores by source

CISA ADP9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: total

References

refcurl.se/docs/CVE-2026-87866.jsonrefcurl.se/docs/CVE-2026-87866.htmlexploithackerone.com/reports/3989514