[XS] Change in openvpn[master]: openvpnserv: fix off-by-one input validation

Attention is currently required from: d12fk, plaisthos.

Hello plaisthos,

I'd like you to do a code review.
Please visit

    http://gerrit.openvpn.net/c/openvpn/+/1888?usp=email

to review the following change.


Change subject: openvpnserv: fix off-by-one input validation
......................................................................

openvpnserv: fix off-by-one input validation

Code checked for a hypothetical third trailing NUL character,
instead of the second. Could read one extra octet beyond the buffer if
it is used up by the data completely.

Discovered and reported by BreachX Zero Day Labs, using Typhon AI Mil v2.
Contributing Researcher: Vivek Parikh.

Reported-by: Vivek Parikh <[email protected]>
CVE: 2026-78221
Change-Id: I1a181d65ad0d5e3765f57373a6ee223ede909dea
Signed-off-by: Heiko Hund <[email protected]>
---
M src/openvpnserv/interactive.c
1 file changed, 1 insertion(+), 1 deletion(-)



  git pull ssh://gerrit.openvpn.net:29418/openvpn refs/changes/88/1888/1

diff --git a/src/openvpnserv/interactive.c b/src/openvpnserv/interactive.c
index 0c6e23f..d2288b9 100644
--- a/src/openvpnserv/interactive.c
+++ b/src/openvpnserv/interactive.c
@@ -2959,7 +2959,7 @@
         const char *rdom = msg->resolve_domains;
         size_t rdom_size = sizeof(msg->resolve_domains);
         size_t rdom_len = strlen(rdom);
-        if (rdom_len && (rdom_len + 1 >= rdom_size || rdom[rdom_len + 2] != 0))
+        if (rdom_len && (rdom_len + 1 >= rdom_size || rdom[rdom_len + 1] != 0))
         {
             return ERROR_MESSAGE_DATA;
         }

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Gerrit-MessageType: newchange
Gerrit-Project: openvpn
Gerrit-Branch: master
Gerrit-Change-Id: I1a181d65ad0d5e3765f57373a6ee223ede909dea
Gerrit-Change-Number: 1888
Gerrit-PatchSet: 1
Gerrit-Owner: cron2 <[email protected]>
Gerrit-Reviewer: d12fk <[email protected]>
Gerrit-Reviewer: plaisthos <[email protected]>
Gerrit-CC: openvpn-devel <[email protected]>
Gerrit-Attention: plaisthos <[email protected]>
Gerrit-Attention: d12fk <[email protected]>

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