VulnerabilityPublished 31 Oct 2026

CVE-2026-119197: Ansible@10 · pyasn1 has quadratic-complexity denial of service in binary REAL decoding

Affects ansible@10Source GCVE Database

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Mentioned vulnerabilities

CVE-2026-59886

Authoritative record:CVE-2026-119197· High 7.5

Not known to be exploited · CVSS 7.5 High · fixed in 0.6.4 : patch ansible@10 soon.

Data as of 31 Oct 2026, 16:51 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	7.5

Patch: Available – fixed in 0.6.4

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Homebrewansible@10`pkg:brew/ansible%4010`Other threats	Affected >=10.6.0	Fixed in–

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Description

## Summary In pyasn1 0.6.4 and earlier, decoding a binary-encoded ASN.1 REAL with a large mantissa can consume CPU time quadratic in the mantissa length. The BER, CER, and DER decoders all use the affected `RealPayloadDecoder`. An application is exposed when it passes attacker-controlled ASN.1 containing a REAL value to one of these decoders, either without an `asn1Spec` or with a schema that includes REAL. The work occurs inside `decode()`; the application does not need to convert, print, or otherwise use the resulting REAL object. This is distinct from [CVE-2026-59886](https://github.com/advisories/GHSA-hm4w-wwcw-mr6r), which concerns converting an already-decoded REAL to a Python float. That issue was fixed in 0.6.4 and its advisory states that decoding alone does not trigger it. ## Root cause and affected components For binary REAL values, [`RealPayloadDecoder.valueDecoder` in v0.6.4](https://github.com/pyasn1/pyasn1/blob/v0.6.4/pyasn1/codec/ber/decoder.py#L535-L603) builds the mantissa one octet at a time: ```python p = 0 while chunk: p <<= 8 p |= chunk[0] chunk = chunk[1:] ``` Each shift processes an integer that grows with the mantissa; with byte strings, each slice also copies the remaining suffix. Repeating both operations for every octet makes decoding quadratic in mantissa size. The decoder's [eight-octet length-field limit](https://github.com/pyasn1/pyasn1/blob/v0.6.4/pyasn1/codec/ber/decoder.py#L1704-L1717) does not impose a practical mantissa-size limit for the inputs demonstrated below. [CER](https://github.com/pyasn1/pyasn1/blob/v0.6.4/pyasn1/codec/cer/decoder.py#L51-L62) and [DER](https://github.com/pyasn1/pyasn1/blob/v0.6.4/pyasn1/codec/der/decoder.py#L23-L31) reuse the BER REAL payload decoder, so all three paths reach this loop. The vulnerable loop is present in every available repository release tag inspected, from v0.2.1 through v0.6.4. Runtime measurements below were made on v0.6.4; older releases were checked for the loop, not benchmarked individually. ## Impact A comparatively small REAL value can hold a decoder worker on one CPU core for seconds or longer. The attacker must be able to supply data that the application sends to an affected decoder, and application-level input limits may reduce exposure. The demonstrated effect is CPU exhaustion during decoding; this advisory does not assert a network endpoint, unauthenticated access, or an affected downstream application by itself. ## Reproduction and evidence The following example uses pyasn1 0.6.4. The `0x09` tag identifies REAL; `0x80 0x00` selects a positive, base-2 binary value with a one-octet zero exponent, followed by a large mantissa. It exercises `decode()` only. ```python import time from pyasn1.codec.ber import decoder as ber from pyasn1.codec.cer import decoder as cer from pyasn1.codec.der import decoder as der def real_value(mantissa_octets): content = b"\x80\x00" + b"\xff" * mantissa_octets length = len(content).to_bytes(3, "big") return b"\x09\x83" + length + content for codec in (ber, cer, der): for size in (50_000, 100_000, 200_000): substrate = real_value(size) started = time.process_time() value, rest = codec.decode(substrate) print(codec.__name__, size, time.process_time() - started) assert not rest assert tuple(value)[1:] == (2, 0) ``` The original report measured the following BER CPU times on repository commit `aa05757`. That commit is later than the official v0.6.4 tag; the vulnerable loop is identical in the tagged release. | Mantissa size | Reporter's BER CPU time | | ---: | ---: | | 50,000 octets | 0.328 s | | 100,000 octets | 1.299 s | | 200,000 octets | 6.043 s | | 400,000 octets | 24.095 s | The same report measured 5.645 s for a 200,000-octet mantissa through DER. A separate local reproduction on the official v0.6.4 tag (`d43496f`, CPython 3.14.8, macOS arm64) measured BER at 0.209 s, 0.884 s, and 3.451 s for 50,000, 100,000, and 200,000 mantissa octets respectively. CER and DER each took about 0.89 s at 100,000 octets. These are machine-specific measurements; the repeated near-fourfold cost for doubled input is the relevant result. Neither reproduction calls `float()`, `str()`, or `prettyPrint()`. ## Fix pyasn1 0.6.5 replaces the per-octet shift and slice loop with one `int.from_bytes(bytes(chunk), "big")` conversion. Sign, scale, exponent, and the decoded REAL tuple are preserved. The fix is in the shared BER payload decoder and therefore covers BER, CER, and DER. A local check of the 0.6.5 candidate decoded a 200,000-octet mantissa correctly through all three codecs; the check does not establish behavior for every application using REAL. ## Workarounds Upgrade to pyasn1 0.6.5. Until then, reject or strictly limit attacker-controlled ASN.1 input that may contain REAL values before passing it to pyasn1. The appropriate size limit depends on the application's available CPU time and request volume.

References

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