Unauthenticated denial-of-service via unbounded HPACK integer decoding in hpax

Weakness Type (CWE)

CWE-407 — CWE-407 Inefficient Algorithmic Complexity

CAPEC

CAPEC-130 — CAPEC-130 Excessive Allocation

CVSS 4.0 Score

8.7

HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Vulnerability description

Inefficient Algorithmic Complexity vulnerability in elixir-mint hpax allows unauthenticated denial-of-service via unbounded HPACK integer decoding.

hpax decodes HPACK variable-length integers with no upper bound on the decoded value or the number of continuation octets. 'Elixir.HPAX.Types':decode_remaining_integer/3 accumulates the integer as int + (value <<< m), shifting by 7 more bits for each continuation octet and stopping only on a terminating octet or truncated input, never because the integer grew too large. Because BEAM integers are arbitrary precision, a run of N continuation octets builds an O(N)-bit bignum and re-adds into an ever-larger bignum on each step, so the total decoding cost is superlinear (about O(N^2)). An unauthenticated attacker who can send an HTTP/2 header block to a server using this decoder (reached through the 'Elixir.HPAX':decode/2 entry point) can supply a small header block that forces a large, attacker-controlled amount of CPU (and transient memory), a denial-of-service amplification.

This issue affects hpax from 0.1.1 before 1.0.4.

Affected

`pkg:hex/hpax`

Module	Source File	Routine
`Elixir.HPAX`	`lib/hpax.ex`	`HPAX.decode/2`
`Elixir.HPAX.Types`	`lib/hpax/types.ex`	`HPAX.Types.decode_integer/2`
		`HPAX.Types.decode_remaining_integer/3`

Status	Type	Version	Changes / Fixed in
affected	semver ^ⓘ	`0.1.1`	< `1.0.4`

`pkg:github/elixir-mint/hpax`

Module	Source File	Routine
`Elixir.HPAX`	`lib/hpax.ex`	`HPAX.decode/2`
`Elixir.HPAX.Types`	`lib/hpax/types.ex`	`HPAX.Types.decode_integer/2`
		`HPAX.Types.decode_remaining_integer/3`

Status	Type	Version	Changes / Fixed in
affected	git ^ⓘ	`56db437a7e`	< `1ba4bb2dc9`

References

https://github.com/elixir-mint/hpax/security/advisories/GHSA-jj2p-32j7-whj2 vendor-advisory related
https://osv.dev/vulnerability/EEF-CVE-2026-58226 related
https://github.com/elixir-mint/hpax/commit/1ba4bb2dc91e80089cf89c73970ac3ded76f17eb patch

Credits

Finder: Peter Ullrich
Remediation developer: Andrea Leopardi
Analyst: Jonatan Männchen / EEF
Analyst: Eric Meadows-Jönsson

CVE record as JSON: GET /cves/CVE-2026-58226.json
OSV record as JSON: GET /osv/EEF-CVE-2026-58226.json