Skip to content

Decimal: Unbounded exponent in `Decimal.new` enables unauthenticated DoS

Moderate severity GitHub Reviewed Published May 7, 2026 in ericmj/decimal • Updated May 12, 2026

Package

erlang decimal (Erlang)

Affected versions

>= 0.1.0, < 3.0.0

Patched versions

3.0.0

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.

References

@ericmj ericmj published to ericmj/decimal May 7, 2026
Published by the National Vulnerability Database May 7, 2026
Published to the GitHub Advisory Database May 12, 2026
Reviewed May 12, 2026
Last updated May 12, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(26th percentile)

Weaknesses

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

CVE ID

CVE-2026-32686

GHSA ID

GHSA-rhv4-8758-jx7v

Source code

Credits

Dependabot alerts are not supported on some or all of the ecosystems on this advisory.

Learn more about GitHub language support

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.