Security research · CVE-2026-119197
pyasn1 has quadratic-complexity denial of service in binary REAL decoding
Published Oct 30, 2026 · catalog updated Oct 30, 2026 · pyasn1 has quadratic-complexity denial
Last checked Nov 6, 2026. A connected source was read within the last 7 days.
Check if you run it
No confirmed exploitation is on record for CVE-2026-119197. EPSS is 0.43%. Act only if a listed version of pyasn1 has quadratic-complexity denial is installed.
Gaps on this record
- The stored product name is a package slug. The name on this page is taken from the title (pyasn1 has quadratic-complexity denial).
- No vendor fix or required action is stored. Compare the linked advisory before you change production.
- Severity
- High7.5
- Known exploitation
- Not in CISA/VulnCheck KEV
- EPSS
- 0.43%
- Remediation
- Version ranges on file
- Affected products
- PyPI pyasn1 · pip pyasn1 · pypi pyasn1
## 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 . An application is exposed when it passes attacker-controlled ASN.1 containing a REAL value to one of these decoders, either without an or with a schema that includes REAL. The work occurs inside ; 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, [ 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: 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
Are you affected?
Enter the version you run. The result uses only the ranges stored on this record.
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- PyPI pyasn10 → 0.6.5
- pip pyasn1<= 0.6.4
- pypi pyasn1version unspecified
How to fix CVE-2026-119197
Upgrade
CVE-2026-119197 lists a fix boundary at 0.6.5. Compare the installed build with that boundary before you change production.
Version check
Affected <= 0.6.4
Advisory
Open the cve_org record and follow its fix.
Official advisories
What to do
Three questions, each answered from this record only. Confirm the vendor advisory before you patch.
Should you patch?
No confirmed exploitation is on record for CVE-2026-119197. EPSS is 0.43%. Act only if a listed version of pyasn1 has quadratic-complexity denial is installed.
Which versions are affected?
Compare what you have installed with 0 → 0.6.5, <= 0.6.4. Compare the installed version with the linked vendor advisory before you change production.
What should an analyst verify?
CWE-407. EPSS 0.43%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Oct 30, 2026 · GitHub Advisory Database
Detected
## 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 . An application is exposed when it passes attacker-controlled ASN.1 containing a REAL value to one of these decoders, either without an or with a schema that includes REAL. The work occurs insi
Oct 30, 2026 · GitHub Advisory Database
Updated
## 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 . An application is exposed when it passes attacker-controlled ASN.1 containing a REAL value to one of these decoders, either without an or with a schema that includes REAL. The work occurs insi
Oct 30, 2026 · PyPA Advisory Database
Fix available
pyasn1 fixed in 0.6.5
Oct 30, 2026 · PyPA Advisory Database
Fix available
pyasn1 fixed in 0.6.5
Oct 30, 2026 · PyPA Advisory Database
Updated
## 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 . An application is exposed when it passes attacker-controlled ASN.1 containing a REAL value to one of these decoders, either without an or with a schema that includes REAL. The work occurs insi
Sources
- CVE.orgVulnerability recordCVE-2026-119197
Official CVE identifier
cve.org - GitHub Advisory DatabasePackage advisoryGHSA-mm57-4v3p-rchx
pyasn1 has quadratic-complexity denial of service in binary REAL decoding
github.com - GitLab Advisory DatabasePackage advisoryCVE-2026-119197
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
advisories.gitlab.com - PyPA Advisory DatabasePackage advisoryGHSA-mm57-4v3p-rchx
pyasn1 has quadratic-complexity denial of service in binary REAL decoding
osv.dev
References
Freshness
Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.
- GitHub Advisory DatabaseNov 6, 2026
- GitLab Advisory DatabaseNov 3, 2026
- PyPA Advisory DatabaseNov 2, 2026
- CVE.orgOct 31, 2026