CVE-2026-25480

FileStore maps cache keys to filenames using Unicode NFKD normalization and ord() substitution without separators, creating key collisions. When FileStore is used as response-cache backend, an unauthenticated remote attacker can trigger cache key collisions via crafted paths, causing one URL to serve cached responses of another (cache poisoning/mixup)

Details

litestar.stores.file._safe_file_name() normalizes input with unicodedata.normalize("NFKD", name) and builds the filename by concatenating c if alphanumeric else str(ord(c)) (no delimiter).
This transformation is not injective, e.g.:

• "k-" and "k45" both become "k45" (because - ord('-') == 45)
• "k/\n" becomes "k4710", colliding with "k4710"
• "K" (Kelvin sign) normalizes to "K", colliding with "K"

When used in response caching, the default cache key includes request path and sorted query params, which are attacker-controlled.

PoC

import asyncio, tempfile
from litestar.stores.file import FileStore

async def main():
    d = tempfile.mkdtemp(prefix="ls_filestore_poc_")
    store = FileStore(d, create_directories=True)
    await store.__aenter__()

    # 1) ASCII ord-collision: "-" -> 45
    await store.set("k-", b"A")
    v = await store.get("k45")
    print("k-  ->", v)
    print("k45 ->", await store.get("k45"))
    if v == b"A":
        print("VULNERABLE: 'k-' collides with 'k45'")

    # 2) NFKD collision: Kelvin sign -> K
    await store.set("K", b"B")   # U+212A
    v2 = await store.get("K")
    print("K ->", await store.get("K"))
    print("K ->", v2)
    if v2 == b"B":
        print("VULNERABLE: 'K' collides with 'K' (NFKD)")

if __name__ == "__main__":
    asyncio.run(main())

Vulnerability type: cache poisoning / cache key collision.
Impacted deployments: applications using Litestar response caching with FileStore backend (or any attacker-influenced keying into FileStore).
Possible impact: serving incorrect cached content across distinct URLs, potential confidentiality/integrity issues depending on what endpoints are cached.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-25480 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no 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. A fixed version is available (2.20.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-25480? CVE-2026-25480 is a medium-severity improper input validation vulnerability in litestar (pip), affecting versions = 2.19.0. It is fixed in 2.20.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-25480? CVE-2026-25480 has a CVSS score of 6.5 (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 litestar are affected by CVE-2026-25480? litestar (pip) versions = 2.19.0 is affected.
4. Is there a fix for CVE-2026-25480? Yes. CVE-2026-25480 is fixed in 2.20.0. Upgrade to this version or later.
5. Is CVE-2026-25480 exploitable, and should I be worried? Whether CVE-2026-25480 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-2026-25480 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-2026-25480? Upgrade litestar to 2.20.0 or later.