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feat: Don't affect MimeMessage with "From" and secured headers from encrypted unsigned messages

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If a message is encrypted, but unsigned:
- Don't set `MimeMessage::from_is_signed`.
- Remove "secure-join-fingerprint" and "chat-verified" headers from `MimeMessage`.
- Minor: Preserve "Subject" from the unencrypted top level if there's no "Subject" in the encrypted
  part, this message is displayed w/o a padlock anyway.

Apparently it didn't lead to any vulnerabilities because there are checks for
`MimeMessage::signatures.is_empty()` in all necessary places, but still the code looked dangerous,
especially because `from_is_singed` var name didn't correspond to its actual value (it was rather
`from_is_encrypted_maybe_signed`).
This commit is contained in:
iequidoo
2023-11-18 21:46:55 -03:00
committed by iequidoo
parent 9cc9579b2d
commit ebfbc11973
5 changed files with 148 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
src/mimeparser.rs
View File

@@ -259,9 +259,9 @@ impl MimeMessage {
}
}
// remove headers that are allowed _only_ in the encrypted part
headers.remove("secure-join-fingerprint");
headers.remove("chat-verified");
// Remove headers that are allowed _only_ in the encrypted+signed part. It's ok to leave
// them in signed-only emails, but has no value currently.
Self::remove_secured_headers(&mut headers);
let from = from.context("No from in message")?;
let private_keyring = load_self_secret_keyring(context).await?;
@@ -305,10 +305,11 @@ impl MimeMessage {
content
});
if let (Ok(mail), true) = (mail, encrypted) {
// Handle any gossip headers if the mail was encrypted. See section
// "3.6 Key Gossip" of <https://autocrypt.org/autocrypt-spec-1.1.0.pdf>
// but only if the mail was correctly signed:
if !signatures.is_empty() {
// Handle any gossip headers if the mail was encrypted. See section
// "3.6 Key Gossip" of <https://autocrypt.org/autocrypt-spec-1.1.0.pdf>
// but only if the mail was correctly signed. Probably it's ok to not require
// encryption here, but let's follow the standard.
let gossip_headers = mail.headers.get_all_values("Autocrypt-Gossip");
gossiped_addr = update_gossip_peerstates(
context,
@@ -318,6 +319,9 @@ impl MimeMessage {
gossip_headers,
)
.await?;
// Remove unsigned subject from messages displayed with padlock.
// See <https://github.com/deltachat/deltachat-core-rust/issues/1790>.
headers.remove("subject");
}
// let known protected headers from the decrypted
@@ -325,24 +329,20 @@ impl MimeMessage {
// Signature was checked for original From, so we
// do not allow overriding it.
let mut signed_from = None;
// We do not want to allow unencrypted subject in encrypted emails because the
// user might falsely think that the subject is safe.
// See <https://github.com/deltachat/deltachat-core-rust/issues/1790>.
headers.remove("subject");
let mut inner_from = None;
MimeMessage::merge_headers(
context,
&mut headers,
&mut recipients,
&mut signed_from,
&mut inner_from,
&mut list_post,
&mut chat_disposition_notification_to,
&mail.headers,
);
if let Some(signed_from) = signed_from {
if addr_cmp(&signed_from.addr, &from.addr) {
if let (Some(inner_from), true) = (inner_from, !signatures.is_empty()) {
if addr_cmp(&inner_from.addr, &from.addr) {
from_is_signed = true;
} else {
// There is a From: header in the encrypted &
@@ -360,6 +360,8 @@ impl MimeMessage {
}
}
if signatures.is_empty() {
Self::remove_secured_headers(&mut headers);
// If it is not a read receipt, degrade encryption.
if let (Some(peerstate), Ok(mail)) = (&mut decryption_info.peerstate, mail) {
if message_time > peerstate.last_seen_autocrypt
@@ -1377,6 +1379,11 @@ impl MimeMessage {
.and_then(|msgid| parse_message_id(msgid).ok())
}
fn remove_secured_headers(headers: &mut HashMap<String, String>) {
headers.remove("secure-join-fingerprint");
headers.remove("chat-verified");
}
fn merge_headers(
context: &Context,
headers: &mut HashMap<String, String>,