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.
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| elixir-mint | hpax | unaffected |
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| elixir-mint | hpax | unaffected |
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Mon, 06 Jul 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | Unauthenticated denial-of-service via unbounded HPACK integer decoding in hpax | |
| First Time appeared |
Elixir-mint
Elixir-mint hpax |
|
| Weaknesses | CWE-407 | |
| CPEs | cpe:2.3:a:elixir-mint:hpax:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Elixir-mint
Elixir-mint hpax |
|
| References |
| |
| Metrics |
cvssV4_0
|
MITRE
Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-07-06T09:03:47.374Z
Reserved: 2026-06-29T18:54:08.633Z
Link: CVE-2026-58226
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