vulnerability / NVI-00012935 / Revision 2
Plug: quadratic-time decoding of nested query/body parameters enables denial of service
GitHub lists this reviewed advisory for plug, plug, plug, plug, plug. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
8.7 HIGH (4.0)
6b3ad84c-e1a6-4bf7-a703-f496b71e49db severity; no combined Null risk score.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
plug
source listed>= 1.15.0, < 1.15.5
### Summary 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
plug
source listed>= 1.16.0, < 1.16.4
### Summary 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
plug
source listed>= 1.17.0, < 1.17.2
### Summary 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
plug
source listed>= 1.18.0, < 1.18.3
### Summary 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
plug
source listed>= 1.19.0, < 1.19.3
### Summary 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
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. NIST National Vulnerability Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-j43x-5hjq-rgxf ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-54892 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.