GHSA-v53p-9fqp-m79j: High severity npm/nodemailer vulnerability
Summary
When addressparser finds no address by its strict reading, it falls back to pulling one out of the free text with /\s\b[^@\s]+@[^\s]+\b\s/. That pattern backtracks quadratically: [^@\s]+ is retried from every offset and rescans the run to the next @ each time. A single header value holding a long whitespace-free run with no usable @ blocks the Node.js event loop for tens of seconds.
It is cheaper to exploit than GHSA-prgh-xp8r-p3m5: 273KB is enough for ~43s, where the comment-joined shape needed ~1.5MB for ~10s.
Details
The fallback in src/addressparser/index.ts ran the pattern as a search. [^@\s]+ crosses neither whitespace nor @, so from each start offset it scans forward to the next @ or to the end of the run and then fails, and the engine simply advances one character and repeats. Three shapes make every offset fail:
- the run holds no @ at all - the only @ has nothing after it - the only @ has nothing before it
A fourth reaches it with a valid address present but placed past a long run, so the long run is walked before the match is found.
PoC
js const addressparser = require('nodemailer/lib/addressparser'); const s = Date.now(); addressparser(' >' + '>[x][x]'.repeat(40000)); // 273KB console.log(Date.now() - s, 'ms'); // ~43000 ms, blocking
Measured on 10.0.5:
| Value | Parse time | | --- | --- | | '[x]'.repeat(40000) (117KB) | 9.0 s | | '[x]'.repeat(40000) + '@' (117KB) | 8.9 s | | '@' + '[x]'.repeat(40000) (117KB) | 8.8 s | | ' >' + '>[x][x]'.repeat(40000) (273KB) | 42.9 s |
Impact
Algorithmic-complexity denial of service. Node is single threaded, so the block stalls the whole process. Reachable without authentication anywhere inbound header values are handed to this parser, mailparser being the notable case, and reachable from application input wherever a user-supplied string is used as a message address, since mime-node parses to, from and cc when composing.
Patch
The search is replaced by a single linear pass that finds the one offset the pattern can match at, which is then applied there with a sticky regex. Match results are unchanged, verified against the previous implementation over 3.4 million random strings comparing both the match offset and the matched text, plus 800k full-parse comparisons.
Found while validating the report in GHSA-prgh-xp8r-p3m5, not reported externally.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/nodemailerto a version that resolves this vulnerability.Fixed in 10.0.6
Event History
Frequently Asked Questions
Who is exposed to this issue?
Applications using npm/nodemailer that pass attacker-controlled email header values to addressparser are exposed. An unauthenticated remote attacker can trigger the issue over the network when they can supply a crafted header value.
What input is needed to trigger the denial of service?
The attacker needs a long whitespace-free string that causes addressparser's fallback expression to search unsuccessfully or inefficiently. Examples include a run with no @ character, an @ with nothing before or after it, or a valid address placed after a long whitespace-free run.
What is the operational impact?
Processing the crafted value can block the Node.js event loop, causing denial of service. The advisory reports that a 273 KB input can block it for about 43 seconds.
How can exposure be reduced if an update cannot be applied immediately?
Reject or strictly limit the length of untrusted email header values before they reach addressparser, especially long whitespace-free runs. Avoid passing attacker-controlled address fields directly to the parser.