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gtls: verify OCSP response signature in gtls_verify_ocsp_status

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Since aeb1a281ca ("gtls: fix OCSP stapling management"), the function
parses the stapled OCSP response and reads the certificate status via
gnutls_ocsp_resp_get_single(), but never calls gnutls_ocsp_resp_verify()
or gnutls_ocsp_resp_verify_direct(). A response with a forged or
corrupted signature is accepted without question.

Fix by calling gnutls_ocsp_resp_verify() against the trust list obtained
from the session credentials immediately after gnutls_ocsp_resp_import().
This handles both directly-signed responses and delegated OCSP responders
without requiring the issuer certificate to be present in the peer chain.

The missing check only affects the CURLOPT_SSL_VERIFYSTATUS code path
when CURLOPT_SSL_VERIFYPEER is disabled. With peer verification enabled,
gnutls_certificate_verify_peers2() independently catches the invalid
response via GNUTLS_CERT_INVALID_OCSP_STATUS before
gtls_verify_ocsp_status() is reached. As a result, no attack is possible
that is not already trivially achievable without OCSP stapling when peer
verification is off. This is a correctness and consistency fix, not a
security vulnerability.

Reported-by: Joshua Rogers

Closes #21677
This commit is contained in:
Joshua Rogers 2026-05-19 15:54:30 +02:00 • committed by Daniel Stenberg
parent d191de891a
commit be6c4ee7fa
No known key found for this signature in database
GPG key ID: 5CC908FDB71E12C2
1 changed files with 17 additions and 4 deletions
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21
lib/vtls/gtls.c
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@ -1429,6 +1429,9 @@ static CURLcode gtls_verify_ocsp_status(struct Curl_easy *data,
{
gnutls_ocsp_resp_t ocsp_resp = NULL;
gnutls_datum_t status_request;
gnutls_certificate_credentials_t creds = NULL;
gnutls_x509_trust_list_t tlist = NULL;
unsigned int verify_status = 0;
gnutls_ocsp_cert_status_t status = GNUTLS_OCSP_CERT_UNKNOWN;
gnutls_x509_crl_reason_t reason;
CURLcode result = CURLE_OK;
@ -1461,13 +1464,23 @@ static CURLcode gtls_verify_ocsp_status(struct Curl_easy *data,
goto out;
}
rc = gnutls_ocsp_resp_get_single(ocsp_resp, 0, NULL, NULL, NULL, NULL,
&status, NULL, NULL, NULL, &reason);
if(rc < 0) {
failf(data, "Invalid OCSP response received");
if(!gnutls_credentials_get(session, GNUTLS_CRD_CERTIFICATE,
(void **)&creds))
gnutls_certificate_get_trust_list(creds, &tlist);
if(!tlist) {
failf(data, "OCSP response signature verification failed");
result = CURLE_SSL_INVALIDCERTSTATUS;
goto out;
}
rc = gnutls_ocsp_resp_verify(ocsp_resp, tlist, &verify_status, 0);
if(rc < 0 || verify_status) {
failf(data, "OCSP response signature verification failed");
result = CURLE_SSL_INVALIDCERTSTATUS;
goto out;
}
(void)gnutls_ocsp_resp_get_single(ocsp_resp, 0, NULL, NULL, NULL, NULL,
&status, NULL, NULL, NULL, &reason);
switch(status) {
case GNUTLS_OCSP_CERT_GOOD: