{"schema_version":"1.9.0","id":"GHSA-2qrf-pqgx-qh9v","published":"2026-10-23T20:46:12Z","modified":"2026-10-23T21:00:04.322993195Z","aliases":["CVE-2026-115774"],"summary":"Twisted: Denial of Service in the Twisted IMAP4 Server via a Negative Literal Size in SEARCH","details":"## Summary\n\nAn infinite-loop vulnerability (CWE-835) in the Twisted IMAP4 server lets an authenticated client freeze the whole process with one small command. `twisted.mail.imap4.parseNestedParens` reads an IMAP literal size with `int()` and never rejects a negative value. A negative size such as `{-100}` drives the parser cursor negative, and because a negative Python index wraps around the end of the string instead of raising, the scanning loop never terminates. It runs synchronously on the single-threaded reactor, so one `SEARCH` command holds the reactor at full CPU forever and every other connection stops being served.\n\n## Details\n\nMeeting an inline literal, `parseNestedParens` reads the size between the braces and advances the cursor past the body:\n\n```python\n# twisted/mail/imap4.py  parseNestedParens\nliteralSize = int(s[i + 1 : end])          # no sign check\ncontentStack[-1].append((s[end + 3 : end + 3 + literalSize],))\ni = end + 3 + literalSize                    # negative size -> i goes negative\n```\n\n`int(b\"-100\")` is `-100`, so `i` goes negative; the loop condition `i < len(s)` stays true and `s[i : i + 1]` on a negative index never raises, so the cursor cycles forever. The `_literalStringLimit` guard only covers the synchronizing-literal continuation path, not this inline branch. The call is reached from `select_SEARCH` through `arg_searchkeys`, dispatched only in the selected state, so a valid login and a selected mailbox (any low-privilege account) suffice. It runs in the reactor thread, and the connection timeout cannot fire because the reactor itself is frozen.\n\nAffected product: Twisted (`twisted.mail`), the IMAP4 server `twisted.mail.imap4.IMAP4Server`\nAffected versions: 26.4.0 and earlier\n\n## PoC\n\nLog in, select a mailbox, and send a `SEARCH` whose literal size is negative:\n\n```text\nC: t1 LOGIN testuser password-test\nC: t2 SELECT INBOX\nC: t3 SEARCH {-100}zzzzzzzzzz\n```\n\nThe server never responds and one core stays at 100 percent. In a measured run a health service co-hosted on the same reactor stopped answering the instant the command arrived, showing the freeze hits the whole process and not just the attacking connection. A valid `{5}zzzzz` completes normally and a non-numeric `{abc}` is rejected with a parse error, which isolates the cause to the missing negative-size check.\n\n## Impact\n\nA remote denial of service. One command of about ten bytes freezes the single-threaded reactor, so it stops serving not only every other IMAP connection but every other service co-hosted in the same process (for example SMTP and POP3 under `twistd mail`), and no timeout can recover it until the process is restarted. It requires an authenticated session, so any account holder can trigger it; there is no confidentiality or integrity impact and no code execution.","affected":[{"package":{"name":"twisted","ecosystem":"PyPI","purl":"pkg:pypi/twisted"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"26.10.0rc1"}]}],"versions":["1.0.1","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.1.0","1.1.1","1.2.0","10.0.0","10.1.0","10.2.0","11.0.0","11.1.0","12.0.0","12.1.0","12.2.0","12.3.0","13.0.0","13.1.0","13.2.0","14.0.0","14.0.1","14.0.2","15.0.0","15.1.0","15.2.0","15.2.1","15.3.0","15.4.0","15.5.0","16.0.0","16.1.0","16.1.1","16.2.0","16.3.0","16.3.1","16.3.2","16.4.0","16.4.1","16.5.0","16.5.0rc1","16.5.0rc2","16.6.0","16.6.0rc1","16.7.0rc1","16.7.0rc2","17.1.0","17.1.0rc1","17.5.0","17.9.0","17.9.0rc1","18.4.0","18.4.0rc1","18.7.0","18.7.0rc1","18.7.0rc2","18.9.0","18.9.0rc1","19.10.0","19.10.0rc1","19.2.0","19.2.0rc1","19.2.0rc2","19.2.1","19.7.0","19.7.0rc1","2.1.0","2.4.0","2.5.0","20.3.0","20.3.0rc1","21.2.0","21.2.0rc1","21.7.0","21.7.0rc1","21.7.0rc2","21.7.0rc3","22.1.0","22.1.0rc1","22.10.0","22.10.0rc1","22.2.0","22.2.0rc1","22.4.0","22.4.0rc1","22.8.0","22.8.0rc1","23.10.0","23.10.0rc1","23.8.0","23.8.0rc1","24.10.0","24.10.0rc1","24.11.0","24.11.0rc1","24.11.0rc2","24.2.0rc1","24.3.0","24.7.0","24.7.0rc1","24.7.0rc2","25.5.0","25.5.0rc1","26.4.0","26.4.0rc2","8.0.0","8.0.1","8.1.0","8.2.0","9.0.0"],"database_specific":{"last_known_affected_version_range":"<= 26.4.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-2qrf-pqgx-qh9v/GHSA-2qrf-pqgx-qh9v.json"}}],"references":[{"type":"WEB","url":"https://github.com/twisted/twisted/security/advisories/GHSA-2qrf-pqgx-qh9v"},{"type":"WEB","url":"https://github.com/twisted/twisted/pull/12764"},{"type":"WEB","url":"https://github.com/twisted/twisted/commit/3d125548bcbe955007cb97f480bb699a5e074741"},{"type":"PACKAGE","url":"https://github.com/twisted/twisted"},{"type":"WEB","url":"https://github.com/twisted/twisted/releases/tag/twisted-26.10.0rc1"}],"database_specific":{"cwe_ids":["CWE-400","CWE-835"],"github_reviewed":true,"github_reviewed_at":"2026-10-23T20:46:12Z","nvd_published_at":null,"severity":"MODERATE"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H"}]}