CVE-2026-103415
When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second…
- Risk score
- 65/100
- CVSS
- 9.3 v4.0
- Exploit chance (30 days)
- 0.3%
- Published
- 14 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second ClientHello without checking that the cookie fits in the outgoing packet. Both the length and the contents of that cookie come from the peer, and the write happens before certificate authentication completes, so a malici…
- Affected
- See advisory
- Fix
- Apply the vendor's security update; see the linked advisory.
- Exploitation
- No known exploitation
Why it is Amber
- CVSS 9.3 critical
- Remotely exploitable without logging in
References
Original description
When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second ClientHello without checking that the cookie fits in the outgoing packet. Both the length and the contents of that cookie come from the peer, and the write happens before certificate authentication completes, so a malicious or compromised server can overwrite memory past the caller supplied TLS packet buffer without presenting a certificate. Only the client path is affected.
Last activity 14 Oct 2026. Patch Forecast updates every hour.