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Decimal: Unbounded exponent in `Decimal.new` enables unauthenticated DoSGHSA-rhv4-8758-jx7v

Fix: ericmj/decimal@6a523f3

GHSA-rhv4-8758-jx7v is a Uncontrolled Resource Consumption vulnerability in decimal. A fix is available for decimal — see the affected versions and patch details below.

Also known asCVE-2026-32686EEF-CVE-2026-32686
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for GHSA-rhv4-8758-jx7v.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs42th percentile — riskier than 42% of all scored CVEsHighest risk
0.00%0.33%0.66%0.98%0.0%0.5%Jun 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected
💧decimal

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.

Description

Summary decimal doesn't bound the exponent on parsed input, so something like "1e10000000" is parsed fine but then explodes the memory to more than 7GB if you run e.g. Decimal.add(Decimal.parse("1e10000000"), 1) because for positive exp, the function tail-recurses with coef * 10 and exp - 1 per iteration, growing the bignum coefficient by one digit each step. In the worst case, one request is enough to OOM the BEAM.

Details

Decimal.new/parse/cast happily store huge exponents. After that, a bunch of core paths allocate proportional to exp:

  • add/sub/div go through add_align, which calls pow10(exp1 - exp2) and builds a giant bignum (lib/decimal.ex:1734-1738, 1827).
  • to_string/2 with :normal (also :xsd and the String.Chars impl) does :lists.duplicate(exp, ?0) (lib/decimal.ex:1506, 1513).
  • to_integer/1 recurses coef * 10, exp - 1 once per unit of exp (lib/decimal.ex:1603-1605).
  • round/3 does the same :lists.duplicate trick on the exp difference (lib/decimal.ex:1850, 1874).
  • compare/3 with a threshold argument loops back into add/sub, so it's vulnerable too (lib/decimal.ex:331-332).

PoC

Any of these will hang or OOM the BEAM:

Decimal.add(Decimal.new("1"), Decimal.new("1e1000000000"))
Decimal.to_string(Decimal.new("1e1000000000"), :normal)
Decimal.to_integer(Decimal.new("1e1000000000"))
Decimal.round(Decimal.new("1e1000000000"))

Impact

Unauthenticated remote DoS. Anything that takes a user-supplied decimal (JSON, form field, Ecto :decimal field — basically everywhere) and then does arithmetic, rounding, to_integer, or to_string on it is exposed. One request can kill the node with a Out-of-Memory exception.

Note on the security fixes done in version 2.4.0

While 2.4.0 has the changes to mitigate this issue it's not considered as a patched version because it doesn't have them enabled by default.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💧Hexdecimal≥ 0.1.0&&< 3.0.03.0.0mix deps.update decimal

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for decimal, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update decimal to 3.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rhv4-8758-jx7v is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

Summary `decimal` doesn't bound the exponent on parsed input, so something like `"1e10000000"` is parsed fine but then explodes the memory to more than 7GB if you run e.g. `Decimal.add(Decimal.parse("1e10000000"), 1)` because for positive `exp`, the function tail-recurses with `coef * 10` and `exp - 1` per iteration, growing the bignum coefficient by one digit each step. In the worst case, one request is enough to OOM the BEAM. ### Details `Decimal.new/parse/cast` happily store huge exponents. After that, a bunch of core paths allocate proportional to `exp`: - `add/sub/div` go through `add_al
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