Summary
Plug: quadratic-time decoding of nested query/body parameters enables denial of service
Plug's nested-parameter decoder (Plug.Conn.Query) parses URL-encoded keys in time quadratic in their bracket-nesting depth. Any unauthenticated remote attacker that can reach a Plug-based HTTP endpoint can pin a BEAM scheduler for minutes with a single small request.
Details
For a key like a[a][a]...=1, Plug.Conn.Query.split_keys/6 (in lib/plug/conn/query.ex) builds an accumulator of :binary.part prefixes (a, a[a], a[a][a], …) that grow ~3 bytes per level. Plug.Conn.Query.insert_keys/3 then does one Map.put per level keyed on that growing prefix, hashing the full byte range each time, and Plug.Conn.Query.finalize_pointer/2 repeats the prefix-keyed walk to materialize the structure. Total cost is O(N²) in nesting depth.
The same code path handles query strings, application/x-www-form-urlencoded bodies, and multipart field names via Plug.Conn.Query.decode/4 and decode_each/2. The default Plug.Parsers.URLENCODED cap is 1 MB (~333,000 nesting levels), but Plug.Parsers accepts urlencoded payloads up to its overall body limit (20 MB by default), so an attacker can scale the per-request work well beyond the urlencoded-specific cap. The decoder shows ~4× scaling per 2× input (16k levels ≈ 195 ms on a single scheduler).
PoC
- POST
a[a][a]...[a]=1asapplication/x-www-form-urlencodedto any endpoint of a Plug-based app. Even at the 1 MB urlencoded-parser default the payload carries ~333,000 nesting levels; with the broaderPlug.Parsersbody limit (20 MB default) a single request can carry millions. - Launch one such request per scheduler concurrently. Each pins a scheduler for minutes; legitimate traffic stalls once all schedulers are busy.
References
Impact
A single low-bandwidth sender can render any internet-reachable Plug-based service (most Phoenix and standalone Elixir/Erlang web stacks) unresponsive. No credentials, specific endpoint, or prior knowledge of the application is required.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
plug to 1.15.5 or later; plug to 1.16.4 or later; plug to 1.17.2 or later; plug to 1.18.3 or later; plug to 1.19.3 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-54892? CVE-2026-54892 is a high-severity security vulnerability in plug (erlang), affecting versions >= 1.15.0, < 1.15.5. It is fixed in 1.15.5, 1.16.4, 1.17.2, 1.18.3, 1.19.3.
- Which versions of plug are affected by CVE-2026-54892? plug (erlang) versions >= 1.15.0, < 1.15.5 is affected.
- Is there a fix for CVE-2026-54892? Yes. CVE-2026-54892 is fixed in 1.15.5, 1.16.4, 1.17.2, 1.18.3, 1.19.3. Upgrade to this version or later.
- Is CVE-2026-54892 exploitable, and should I be worried? Whether CVE-2026-54892 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
- What actually determines whether CVE-2026-54892 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.
- How do I fix CVE-2026-54892?
- Upgrade
plugto 1.15.5 or later - Upgrade
plugto 1.16.4 or later - Upgrade
plugto 1.17.2 or later - Upgrade
plugto 1.18.3 or later - Upgrade
plugto 1.19.3 or later
- Upgrade