CVE-2026-91777 jackson-databind: quadratic forward-reference completion in Collection and Map deserializers
Attackers can cause CPU exhaustion via quadratic complexity in jackson-databind deserialization of identity-enabled collections or maps.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-91777?
CVE-2026-91777 is a high-severity denial of service vulnerability in FasterXML jackson-databind, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Forward-reference completion for @JsonIdentityInfo object IDs in FasterXML jackson-databind performs a linear scan of the pending-reference accumulator for every resolved ID. The affected paths are CollectionDeserializer.CollectionReferringAccumulator.resolveForwardReference() and the equivalent implementation in MapDeserializer. When a document first creates N unresolved object-ID references in an identity-enabled collection or map and then defines those same IDs in reverse order, completion performs on the order of N * (N + 1) / 2 identity comparisons, so a shallow document whose size grows linearly causes quadratic CPU work during deserialization. The reporter instrumented equals() calls on the ID class and measured exactly 2,003,000 comparisons at N = 2,000, against zero comparisons in the pending-reference lookup path for an equally sized control in which every reference was already resolved. The input requires no deep nesting and no syntactically unusual JSON. Exploitation requires an application that deserializes attacker-influenced JSON into an identity-enabled collection or map. The fix replaces the repeated linear lookup with a keyed pending-reference structure.
Weakness: CWE-400
Which versions are affected by CVE-2026-91777?
10 open source packages ship an affected version, including com.fasterxml.jackson.core:jackson-databind and tools.jackson.core:jackson-databind.
| Package | Affected | Fixed in |
|---|---|---|
com.fasterxml.jackson.core:jackson-databind Maven | From 2.19.0 | 2.21.7 |
com.fasterxml.jackson.core:jackson-databind Maven | From 2.19.0 | 2.21.7 |
com.fasterxml.jackson.core:jackson-databind Maven | From 2.22.0 | 2.22.3 |
com.fasterxml.jackson.core:jackson-databind Maven | From 2.22.0 | 2.22.3 |
com.fasterxml.jackson.core:jackson-databind Maven | From 2.5.0 | 2.18.11 |
com.fasterxml.jackson.core:jackson-databind Maven | From 2.5.0 | 2.18.11 |
4 more packages
tools.jackson.core:jackson-databind Maven | From 3.0.0 | 3.1.7 |
tools.jackson.core:jackson-databind Maven | From 3.0.0 | 3.1.7 |
tools.jackson.core:jackson-databind Maven | From 3.2.0 | 3.2.3 |
tools.jackson.core:jackson-databind Maven | From 3.2.0 | 3.2.3 |
Linux distribution packages (4)
pki-jackson-databind AlmaLinux:9 | All versions | 2.21.6-1.el9_8.1 |
jackson-databind Red Hat:enterprise_linux:9::appstream | All versions | 0:2.21.6-1.el9_8.1 |
pki-jackson-databind Red Hat:enterprise_linux:9::appstream | All versions | 0:2.21.6-1.el9_8.1 |
jackson-databind Rocky Linux:9 | All versions | 0:2.21.6-1.el9_8.1 |
How do I fix CVE-2026-91777?
Upgrade com.fasterxml.jackson.core:jackson-databind to a fixed version for your release line: 2.21.7, 2.22.3 or 2.18.11.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-91777 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-91777 exists.
Sources
Also known as ALSA-2026:85231, CLEANSTART-2026-AJ37436, CLEANSTART-2026-BX50217, CLEANSTART-2026-DY58341, CLEANSTART-2026-EA40241, CLEANSTART-2026-GM79198 and 107 more.