| Package | Affected versions | Patched versions |
|---|---|---|
| browserslist | < 4.28.7 | 4.28.7 |
File: index.js
Location: cache (browserslist()'s result cache, line ~402) and
parseCache (parseQueries()'s AST cache)
var cache = {}
var parseCache = {}
function browserslist(queries, opts) {
...
var cacheKey = JSON.stringify([queries, context])
if (cache[cacheKey]) return cache[cacheKey]
...
if (!env.env.BROWSERSLIST_DISABLE_CACHE) { cache[cacheKey] = result }
return result
}
function parseQueries(queries) {
var cacheKey = JSON.stringify(queries)
if (cacheKey in parseCache) return parseCache[cacheKey]
var result = parseWithoutCache(QUERIES, queries)
if (!env.env.BROWSERSLIST_DISABLE_CACHE) { parseCache[cacheKey] = result }
...
}
Every distinct (queries, context) pair is cached forever — no size cap,
TTL, or eviction. browserslist.clearCaches() never resets either object
(it only resets node.js's own filesystem caches); the only opt-out is the
BROWSERSLIST_DISABLE_CACHE env var, controlled by the calling
application, not an attacker.
Some short, valid queries amplify this badly. The since <year>-<month>-<day>
query type (/^since (\d+)-(\d+)-(\d+)$/i) accepts any digit
combination — Date.UTC() normalizes rather than rejects out-of-range
values — giving an effectively unbounded space of ~17-byte distinct cache
keys, each of which resolves to (and caches) a result close to the full
~8.5 KB browser list for any sufficiently old year.
20,000 distinct since <year>-<month>-<day> queries (~330 KB total input,
--expose-gc before/after measurement to rule out uncollected garbage)
retained over 50 MB of heap permanently — roughly 150x
amplification, growing linearly with no cap observed up to 40,000 queries
(52.3 MB).
Any long-running process (server, daemon, warm CI worker) that calls
browserslist() with a query value that varies across requests/items and is
influenced, even partially, by external input accumulates one cache entry
per distinct value ever seen. An attacker who can influence that value
across many requests (this is a volumetric attack, unlike the
single-request DoS findings from this same research pass) sends a stream of
cheap, distinct queries (e.g. since 1900-01-01, since 1900-01-02, ...)
until the process runs out of memory and crashes.
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freeReplace both plain-object caches with Maps bounded to a fixed maximum
entry count, evicting the oldest entry once the cap is reached (Map
preserves insertion order, so .keys().next().value is always oldest):
var CACHE_MAX_ENTRIES = 500
function boundedCacheSet(map, key, value) {
if (map.size >= CACHE_MAX_ENTRIES) {
map.delete(map.keys().next().value)
}
map.set(key, value)
}
var cache = new Map()
var parseCache = new Map()
(read sites changed to .has()/.get(), write sites to boundedCacheSet())
Verification:
NODE_ENV=test npx uvu test .test.js → 301/301 pass unmodified
(test/cache.test.js exercises clearCaches()/BROWSERSLIST_DISABLE_CACHE
against node.js's separate filesystem caches, unaffected here); confirmed
a repeated identical call still returns the cached reference.since-date queries (was
10.5 → 16.5 → 28.4 → 52.3 MB pre-fix).browserslist() with
query values that vary across requests/items and are influenced by
external input.browserslist @ HEAD (== v4.28.6, current latest stable release) under local
Node.js v20.19.5, run with --expose-gc for accurate heap measurement.
Found during a broader review of this codebase in the same research pass that produced GHSA-rrmg-cfrq-23vv (parse.js algorithmic complexity), GHSA-g6p8-hj8g-x889 (baseline regexp ReDoS), GHSA-73wf-gq98-2v4g (normalizeStats crash/prototype write), and GHSA-h633-868p-5rfw (SCOPED_CONFIG__PATTERN ReDoS) — all single-request DoS vectors. This one is different in character (volumetric, not single-request) and is reported separately/scored lower accordingly.