Affected: Homebrew: alot

### Summary `wildcardToRegexp()` in `twisted/mail/imap4.py` converts IMAP LIST/LSUB wildcard patterns to Python regular expressions. It substitutes the two IMAP wildcards (`*` → `(?:.*?)` and `%` → `(?:(?:[^\\/])*?)`) but passes every other character through unchanged to `re.compile()`. This means that an authenticated IMAP client can send a quoted pattern string containing arbitrary regex syntax - including catastrophic-backtracking constructs such as `(a+)+z`.

Because Twisted runs a cooperative, single-threaded reactor, a blocking regex match freezes **all** I/O on the server for the duration of the match.

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## Vulnerable Code

### `twisted/mail/imap4.py`

```python # line 4595 def wildcardToRegexp(wildcard, delim=None): wildcard = wildcard.replace("*", "(?:.*?)") if delim is None: wildcard = wildcard.replace("%", "(?:.*?)") else: wildcard = wildcard.replace("%", "(?:(?:[^%s])*?)" % re.escape(delim)) return re.compile(wildcard, re.I) # ← user input compiled verbatim ```

```python # line 4993 class MemoryAccountWithoutNamespaces: def listMailboxes(self, ref, wildcard): ref = self._inferiorNames(_parseMbox(ref.upper())) wildcard = wildcardToRegexp(wildcard, "/") # ← user-supplied wildcard return [(i, self.mailboxes[i]) for i in ref if wildcard.match(i)] ``` ---

### Proof of Concept

```python from twisted.mail.imap4 import wildcardToRegexp import time

rx = wildcardToRegexp("(a+)+z", "/") for n in [20,…

Twisted is an event-based framework for internet applications, supporting Python 3.6+. In 25.5.0 and earlier, wildcardToRegexp() in twisted/mail/imap4.py translates the IMAP asterisk and percent wildcards but passes all other characters from an authenticated client's LIST or LSUB pattern directly to re.compile(), allowing nested or otherwise expensive regular expression constructs to cause catastrophic backtracking when matched against mailbox names. Because Twisted uses a cooperative single-threaded reactor, the blocking match suspends all server input and output for the duration of the match. No fixed release is available as of this review.

Affected: PyPI: Twisted

### Summary `wildcardToRegexp()` in `twisted/mail/imap4.py` converts IMAP LIST/LSUB wildcard patterns to Python regular expressions. It substitutes the two IMAP wildcards (`*` → `(?:.*?)` and `%` → `(?:(?:[^\\/])*?)`) but passes every other character through unchanged to `re.compile()`. This means that an authenticated IMAP client can send a quoted pattern string containing arbitrary regex syntax - including catastrophic-backtracking constructs such as `(a+)+z`.

Because Twisted runs a cooperative, single-threaded reactor, a blocking regex match freezes **all** I/O on the server for the duration of the match.

---

## Vulnerable Code

### `twisted/mail/imap4.py`

```python # line 4595 def wildcardToRegexp(wildcard, delim=None): wildcard = wildcard.replace("*", "(?:.*?)") if delim is None: wildcard = wildcard.replace("%", "(?:.*?)") else: wildcard = wildcard.replace("%", "(?:(?:[^%s])*?)" % re.escape(delim)) return re.compile(wildcard, re.I) # ← user input compiled verbatim ```

```python # line 4993 class MemoryAccountWithoutNamespaces: def listMailboxes(self, ref, wildcard): ref = self._inferiorNames(_parseMbox(ref.upper())) wildcard = wildcardToRegexp(wildcard, "/") # ← user-supplied wildcard return [(i, self.mailboxes[i]) for i in ref if wildcard.match(i)] ``` ---

### Proof of Concept

```python from twisted.mail.imap4 import wildcardToRegexp import time

rx = wildcardToRegexp("(a+)+z", "/") for n in [20,…

Affected: Ubuntu:Pro:14.04:LTS: twisted, Ubuntu:Pro:16.04:LTS: twisted, Ubuntu:Pro:18.04:LTS: twisted, Ubuntu:20.04:LTS: twisted, Ubuntu:22.04:LTS: twisted, Ubuntu:24.04:LTS: twisted, Ubuntu:26.04:LTS: twisted

(Twisted is an event-based framework for internet applications, support ...)